Aimee Stephens worked for R.G. & G.R. Harris Funeral Home for six years before beginning her gender transition. Then serving as funeral director and embalmer, she wrote a letter on July 31, 2013, to her employers to share that she would begin wearing appropriate women’s business attire at work. They decided that was unacceptable, and they fired Stephens.

Represented by the Equal Employment Opportunity Commission, Stephens fought back, arguing that firing her because she didn’t conform to her employers’ gender-based stereotype violated Title VII of the Civil Rights Act of 1964, which prohibits sex discrimination. She lost in federal district court in Detroit, but won at the Sixth Circuit Court of Appeals, which covers Michigan, Ohio, Kentucky, and Tennessee.

Stephen’s case was a major first—the first time that the EEOC sued an employer on behalf of a transgender plaintiff and asserted that gender identity discrimination is sex discrimination. Her win made history. Which is why conservatives (backed by 16 states) are lining up to try to get the Supreme Court to reverse it.