Both federal and state law protect employees and applicants from employer retaliation for engaging in activity that is protected by anti-discrimination laws.
You cannot retaliate against employees for participating in activities to further the enforcement of employment discrimination laws. The retaliation prohibition is quite broad and includes retaliation against a person who objected to a practice that is legal but that the person reasonably believed to be illegal. Protection from retaliation is not limited to applicants and employees; it covers all individuals, including former employees.
There are also retaliation protections for whistleblowers.