The law protects employees who complain or oppose any part of employment discrimination. There are laws against an employer retaliating or punishing an employee who comes forward. There is a reason why there are anti-retaliation laws, and that is because these experiences can be very emotional.
When somebody gets called out for violating the human rights law, their knee jerk reaction is to punish and to lash out. According to the US Equal Employment Opportunity Commission, employees should know that there are consequences if they suffer adverse action after they complain, and that they should not fear coming forward if they are being subjected to employment discrimination.
Frequently asked questions about the laws against retaliation would involve what sort of complaint or opposition does the employees need to engage in. The complaint needs to be about something unlawful and something that violates human rights law. So it would have to be a complaint about age discrimination or pregnancy discrimination. It does not have to be in writing. Make sure that the employer receives it and knows what you are complaining about. Something in writing could be helpful, but there is no requirement that there be a written complaint. You do not have to be fired to have a claim.
For retaliation, you have to suffer some form of adverse employment action. It could be a transfer to an undesirable shift, a demotion or a cut in pay. If you make a complaint of employment discrimination, your employers should take it very seriously and look into it. If your employer tries to brush it under the rug, does not investigate, conducts a superficial investigation or tells you it was unsubstantiated, your next step would be to file a retaliation suit.