In 1970, Ruth Bader Ginsburg took up a tax law case that changed the face of gender discrimination law forever.

Felicity Jones plays Ruth Bader Ginsburg in a new movie about the landmark 1972 case that opened the doors to combat discrimination based on gender.

Directed by Mimi Leder (Deep Impact, Pay It Forward) and based on a script by Ginsburg’s nephew, first-time screenwriter Daniel Stiepleman, the film also stars Armie Hammer as Ginsburg’s supportive husband, Marty.

Jones plays the famed Associate Justice of the Supreme Court, depicting her at the start of her academic life in 1956, while being one of the few women at Harvard Law School. At the time, she’s told that she’s “occupying a place at Harvard that could have gone to a man.”

Later, in 1970 while Ginsburg is teaching law at Rutgers Law School, her husband brings her a tax law case that could prove pivotal for sex discrimination cases in the future.

In the case, Charles Moritz was denied a tax deduction for nursing care for his ailing mother so he could work. At the time, Section 214 of the Internal Revenue Code specifically limited the deduction to “a woman, a widower or divorce, or a husband whose wife is incapacitated or institutionalized.”

The court ruled that Moritz, a man who had never married, did not qualify for the deduction. Ruth sees this case as an opportunity to challenge many laws enacted over the years that assume that men will work to provide for the family, and women will stay home and take care of the husband and children. She believes that if she can set a precedent ruling that a man was unfairly discriminated against on the basis of sex, that it can be cited in cases challenging laws discriminating against women.

Particularly, she believes that an appellate court composed entirely of male judges will find it easier to identify with a male appellant in this particular case.

In her own real-life story, Ginsburg would become an icon for gender equality through her continued work against discrimination and the sheer symbolism of her continued success as a woman in her field.

In 1970, she co-founded the Women’s Rights Law Reporter, the first law journal in the U.S. to focus exclusively on women’s rights. She taught at Columbia from 1972 to 1980, where she became the first tenured woman and co-authored the first law school casebook on sex discrimination.

She would go on to co-found the Women’s Rights Project at the American Civil Liberties Union (ACLU), which struck down many gender-based laws, and in 1993 became an associate justice of the United States Supreme Court.

Ginsburg was born in 1933 in Brooklyn, New York, into a first-generation American Jewish family. She studied at Harvard but transferred to Columbia University, where she would also eventually teach law.

The famed judge was also the subject of an acclaimed documentary earlier this year, RGB, which chronicled her life and career over several decades.

On the Basis of Sex premiered in theaters on Dec. 25.