An employer, labor union, or employment agency commits an unlawful employment practice if the employer, labor union, or employment agency retaliates or discriminates against a person who, under this chapter:

1. (1) opposes a discriminatory practice;
2. (2) makes or files a charge;
3. (3) files a complaint; or
4. (4) testifies, assists, or participates in any manner in an investigation, proceeding, or hearing.

Acts 1993, 73rd Leg., ch. 269, Sec. 1, eff. Sept. 1, 1993.