Can I Be Fired as Retaliation for Making an HR Complaint or Because I Become Pregnant?
No.  An employer may not terminate, demote, fail to promote, or otherwise subject an employee to hostile backlash in reaction to an employee engaging in certain protected activities, such as telling your employer that you’re pregnant, or reporting racist treatment, or reporting the sexual harassment of yourself or a co-worker.
If the company reacts by ignoring you or failing to investigate or making your work life worse as a result, that would be considered illegal retaliation, an adverse action that can get an employer successfully sued for wrongful termination.
Other protected activities may include taking maternity or any other disability, FMLA leave or other medical leave, sitting on a jury, serving in the military, taking time off to vote, or participating in an official investigation into the employer's practices by a governmental agency.