What are the criteria which an employer cannot use in order to differentiate the situation of employees?

According to the article 11³ of the Polish Labour Code, the criteria which an employer cannot use in order to differentiate the situation of employees (discrimination criteria) are: 

1. gender,
2. age,
3. disability,
4. race,
5. religion,
6. nationality,
7. political views,
8. trade union membership,
9. ethnic origins,
10. denomination,
11. sexual orientation,
12. employment for a fixed or indefinite time period, full or part time work

Legal status:4th June 2014