Recently, Brenda Feigen's emphasis in the area of Constitutional Law has been on the 14th amendment and sex and sexual orientation discrimination. She has written numerous articles for websites and blogs on the issue. (See the Articles page). After Feigen graduated from Harvard Law School, she worked with the U.S. Senate Subcommittee on Constitutional Amendments to organize the hearings it held on the Equal Rights Amendment. In her capacity as National Vice President of Legislation for NOW, she contacted people and organizations whose testimony would likely convince any skeptical Senators. (It was then that she met Gloria Steinem.) Feigen, herself, testified on behalf of NOW for the ERA. After that amendment was passed and sent out to the states for ratification, she co-authored with her then husband, Marc Fasteau, a seminal article for the Harvard Women's Law Journal that set forth the reasons that states did not retain rights to rescind amendments that they had earlier ratified. In addition to becoming an expert on the constitutional issues raised by same-sex marriage, Feigen represents clients who have been denied basic rights under the first (freedom of speech, religion and press), fourth (right to privacy), fifth (due process), ninth (individual rights) and fourteenth (equality of rights) amendments. She represented a group of women who were suing the Augusta National Golf Club because the city and state were colluding to keep women from joining. Before that, she was one of the plaintiffs and lawyers who successfully sued the Harvard Club of New York City for preventing alumnae from being admitted.

Her fondness for and expertise in constitutional law started at Harvard Law School but became fully developed shortly after graduation when she co-directed the ACLU's Women's Rights Project with now Justice Ruth Bader Ginsburg. Despite the project's name, both Feigen and Ginsburg emphasized the harms caused by discrimination against men, not just women. Feigen's then husband, Marc Fasteau, authored a seminal book on that subject called The Male Machine, (McGraw Hill, 1974). Together they lectured around the country on the importance of removing sex-role stereotypes that harmed men as well as women.

In recent years, Feigen has devoted time to the issues raised by the monumental same-sex marriage cases and their aftermath. Continuing their friendship, she visited with Justice Ginsburg in her Chambers on the afternoons after the Court rendered its ground-breaking decisions in those cases.