According to the “Supplementary Survey for the Economically Active Population Survey” conducted by Statistics Korea, the proportion of non-regular workers remained at around 55–65% from August 2001 to March 2007, began decreasing from August 2007, and reached 43.6% in March 2016 [1]. The proportion is still high compared to the OECD average of 11.1% and the average of 14.4% in European countries [2]. In addition, 96.1% of non-regular workers are either temporary workers or workers who have temporary job elsewhere; hence job stability in Korea can be considered very weak in comparison to that in other countries [1].

In general, non-regular workers can be classified according to type of employment [3]. Classification based on type of employment defines non-regular labor as labor in which the objectives in the contract concluded with the employer differ from that of conventional regular work. Based on this definition, hourly, temporary, daily, and dispatched labor is classified as non-regular labor [3–5]. In fact, there are various types of employment within the non-regular labor category, and because of these, sub-groups can be significantly dissimilar even within the same category [6]. Furthermore, a large gap in working conditions is evident between sub-groups in the non-regular worker group depending on the industry and type of employment [7]. According to the type of employment in non-regular workers, the additional study is requested for the discrimination in the viewpoint of occupational health level.

Discrimination refers to unfair treatment experienced by an individual or group based on their affiliation or status [8]. Discrimination based on type of employment is a good example. According to the recent studies, non-regular workers mostly have poorer working conditions in terms of wages, additional wages, employee benefits, and social security as well as job stability than do regular workers. Furthermore, it is not easy to transition from non-regular employment to regular employment, which tends to be increasingly firmly entrenched [9]. Even in the public sector, a large gap is evident in working conditions between non-regular and regular workers, such as in wages and employee benefits, and it was found that they are frequently given unreasonable work orders [10]. In addition, non-regular workers were reported to have a lower level of health than regular workers across various health indicators such as chronic disease, acute disease, social physiological health, and self-rated health [11]. Sub-contract workers are more likely to experience occupational accidents than regular workers, and some studies have pointed out non-regular employment as a major reason for the occurrence of occupational accidents [12, 13].

In this regard, the law prohibits discrimination based on type of employment. The Act on the Protection, Etc. of Fixed-Term and Part-Time Employees and the Act on the Protection, Etc. of Dispatched Workers state that the employer should not discriminate against fixed-term, part-time (hourly), and dispatched workers in terms of wages and other working conditions without reasonable justification compared to regular workers performing the same or similar work in the business or workplace. These Acts prevent discrimination against non-regular workers based on type of employment and protect their appropriate working conditions. However, discrimination is quite common nonetheless.

Most previous studies on non-regular workers focused on identifying gaps in working conditions such as wages, social security, job security, differences in job satisfaction, and inequality in health by comparing to regular workers [9, 10, 14, 15]. Although there were some studies to investigate on the gaps among non-regular worker, they have focused only on socioeconomic status such as wages or employee benefits, but neglected on health and safety issues. In addition, there are few studies on job factors that affect the experience of discrimination in each type of employment or the association between discrimination and health impact indicators [16, 17]. As such, we intended to examine occupational health characteristics according to discrimination experience and relating factors that affect discrimination experience in the non-regular workers. This study ultimately aimed to determine measures to improve non-regular workers’ discrimination experience and contribute to establishing occupational health policies.

In this study, the discrimination experience rate was significantly higher in male, aged less than 40 years old, above high school graduate than middle school graduate, higher wage level, shorter employment period and larger company’s scale. This demonstrates that various factors such as sex, age, education level, wage, years of employment, and the company’s scale are involved in combination when the worker perceives discrimination. Since there are few existing studies on the factors or mechanisms affecting non-regular workers’ discrimination experience, it is difficult to directly compare or interpret this study’s results. However, preceding researches findings that male and high wage workers were more likely to be exposed to occupational risk factors in non-regular workers [1], and only because on non-regular workers whose income averages at about 1.235 million won in our research, they are more likely demanding high intensity of work and harsh working environment for more wage. So it could be interpreted as such that poor working conditions marked by increased exposure to occupational risk factors have led to having felt discriminated against. This interpretation would be consistent with results from another study that working conditions have an effect on discrimination experience [18]. In addition, women tend to deny their discrimination experience in the workplace more than men and underreport their discrimination experience; therefore, men seem to experience more discrimination [19, 20]. When the education level is higher, the reporting of discrimination experience tends to increase [21]. As the degree to which workers accept social disadvantages arising from their employment conditions could vary, it is possible that they are affected by personal traits in addition to objective working conditions. The results that workers experienced more discrimination when relatively younger in age, have above high school graduate than middle school graduate, and the company’s scale was larger may be due to differences in such personal social standards by which any feeling, including that of discrimination is gauzed, but follow-up research is required to further explore the correlations.

For working conditions according to discrimination experience, the group who experienced discrimination had a higher level of physical, musculoskeletal, and mental occupational risk factors. It seems that poor working conditions affected their discrimination experience, which is consistent with the findings of a previous study that discrimination experience was affected by working conditions [18]. For health impact according to discrimination experience, it was found that the group who experienced discrimination had a higher threat to health and presenteeism. These results are comparable to those of other studies, in feeling of having discriminated could act as both physical and mental stressor that raise blood pressure, increase the occurrence of cardiovascular diseases, cause mental illness such as depression and increase unhealthy behaviors, which in turn would ultimately deteriorate overall health status [22–26].

To identify the factors that affected discrimination experience, this study adjusted for sex, age, education level, wage, average working hours per week, and the company’s scale and characteristics by using binomial logistic regression analysis.

The group who experienced discrimination scored higher for occupational stress, and the one with a high level of occupational stress experienced discrimination 2.31 to 3.5 times more than the one with a low level. In previous studies, non-regular workers had more occupational stress factors than regular workers, a higher level of job demand and job instability, and a lower level of job autonomy, and their compensation system was not appropriate [12, 27, 28], in short such studies have shown that differences in working conditions between the two groups led to differences in the level of occupational stress. It could be considered that discrimination experience could have also influenced occupational stress. However, it is more proper to understand that occupational stresses, such as high level of job demand, interpersonal conflict, job instability and low level of job autonomy, rewards, have increased the incidences of discrimination experiences. But follow-up research is required to further explore the correlations between occupational stress and discrimination experience. As this study found that the percentage of discrimination experience increased among sub-groups in the non-regular group when the level of occupational stress increased, occupational stress must be managed by focusing on those workers who experienced discrimination.

Regarding employment status, temporary and daily workers experienced discrimination 1.45 and 1.83 times more than permanent workers. These results seem to stem from the fact that temporary and daily workers’ job stability is inferior to that of permanent workers, even though they all are, in essence, non-regular workers, which can be substantiated by the results of another study that have shown the level of exposure to risk factors to be different even among non-regular workers, depending on the type of employment: fixed-term, non-fixed term, hourly, temporary agency, and indirect [1]. Differences in job stability and risk factors affected discrimination experience among non-regular workers. In Working Conditions Survey, among non-regular workers, employment status was further classified to permanent (employed longer for a year), temporary (employed longer than a month, but shorter than a year), daily (employed shorter than a month). And among non-regular workers, differences in discrimination experience existed, depending on the status of employment. As such, in order to make a policy for reducing discrimination experiences more efficiently, it is necessary to subclassify non-regular workers.

When work patterns were not consistent, it was about 1.4 times more likely that discrimination would be experienced. It is reckoned that inconsistent working hours and shift work can cause insomnia and interfere with family and social life [29], or a high level of occupational stress from shift work could have an effect [30]. Authors of this study assert that inconsistent work patterns decrease the quality of life while increasing occupational stress and affects discrimination experience.

When support of boss was low, it was about 1.3 times more likely that discrimination would be experienced. Previous studies indicated that the support of boss decreased role conflict and physical stress while boosting confidence [31, 32], and was a protection factor that decreased the experience of a sense of depression [33, 34]. Therefore, the support of boss is considered a factor that decreases discrimination experience, because the boss has more tools and means within the workplace to handle the situation and access to institutional support for workers who experience discrimination [35].

It was found that the group who experienced discrimination had a high level of subjective job instability and a low level of work environment satisfaction. This decreases an individual worker’s productivity, and job commitment and responsibility, which consequently reduces organizational productivity as a whole [36, 37]. Preceding study also suggested that subjective perception of job stability was correlated to job commitment [4]. Thus, it seems sound that aiming to reduce discrimination experience, which could in turn affect subjective job stability to increases job commitment might help to improve collective productivity of organization. Only, this may be influenced by discrimination experiences, but it may affect the experience of discrimination. Follow-up research is required to further explore the correlations.

This study examined occupational health characteristics according to discrimination experience and relating factors that affect discrimination experience. It is worth noting that this study is meaningful in that it presented basic data for policies to reduce discrimination experience of non-regular workers. However, the original purpose of data of the Working Conditions Survey used in this study was to investigate working conditions and identify various forms of risk factors; thus, there were limitations in terms of analyzing factors related to discrimination experience in more depth based on such data. And the information bias might be presented because workers who responded more having discrimination tend to respond having worse outcomes. But to control possible bias, Working Conditions Survey tried to minimize systemic or information bias by implementing random sampling and one on one interview. And it was comprised of ninety questions, of which only one (65th) pertained to the discrimination, the possibility seems to be low for the discriminated workers to respond having worse outcomes. Nevertheless, as this study was cross-sectional, it was limited in that it was difficult to identify a causal relationship and to say that there is no information bias. Also, owing to Working Conditions Survey used in this study was subjective questionnaire, the possibility of exaggerated or unintentional incorrect response cannot be excluded. As such, possible of misclassification for exposures and outcomes cannot be excluded. Therefore, a future study would need to be conducted to supplement this limitation.

Using data of the 4th Korean Working Conditions Survey, this study examined occupational health characteristics according to discrimination experience and relating factors that affect discrimination experience. The demographic and occupational factors were complexly related to discrimination experience in non-regular workers. The experience of discrimination had increased when occupational stress was higher, they were temporary or daily workers rather than permanent workers, work patterns were not consistent, and their boss’ support was low. Improving various relating factors, (e.g. occupational stresses, employment status and occupational characteristics), this would ultimately expect to improve non-regular workers’ discrimination.