In the EEOC's 2015 Enforcement Guidance on Pregnancy Discrimination and Related Issues, the agency made its position clear:
Title VII prohibits discrimination based on pregnancy, childbirth, or a related medical condition. Thus, an employer may not discriminate against a woman with a medical condition relating to pregnancy or childbirth and must treat her the same as others who are similar in their ability or inability to work but are not affected by pregnancy, childbirth, or related medical conditions.… Title VII protects women from being fired for having an abortion or contemplating having an abortion.
The courts universally support the EEOC's position. It's been the law of the 6th Circuit for nearly 20 years, and the 3rd Circuit for 10.
Yes, there are limited exceptions. The First Amendment, for example, might protect religious institutions that take adverse actions against an employee because of an abortion.
For the most part, however, you need understand that whether or not you agree with a woman's right to have an abortion, abortion discrimination equals pregnancy discrimination, and firing an employee who has (or expresses an intent to have) an abortion is no different than firing that employee because of her pregnancy.
* Image by hhach on Pixabay