There was a film adaptation of First Monday in October released in 1981 starring Walter Matthau and Jill Clayburgh, both of whom received Golden Globe nominations for there performances. Unfortunately, it's not all that great of a movie. The play in and of itself is a very idealized view of how SCOTUS works, and the movie Hollywood-izes it even more. Clayburgh in particular seems miscast, and while the scenes between her and Matthau debating cases are the highlight of the movie, they're quickly abandoned in favor of a melodramatic plot. Director Ronald Neame also tries to pump up the sexual tension between Matthau and Clayburgh (read that a few more times) in ia seeming attempt to turn it into a sort of belligerent romcom at times, leading to a completely miscalculated moment in the climax where after Matthau has a speech where he says to Clayburgh that he doesn't think she has any ethical obligation to resign her seat at the Court, she proceeds to kiss him square on the mouth. While that's as far as their "romance" goes, even the possibility of a romantic relationship between Justices would be a major conflict of interest, and that's not brought up at all.
If you're looking for other plays about the Supreme Court, you could also look at The Magnificent Yankee, about Oliver Wendell Holmes (the film adaptation of that play earned Louis Calhern, reprising his role from the Broadway production, an Oscar nomination) or Thurgood, the one man play by George Stevens about Thurgood Marshall whose stage production was filmed, and that earned Laurence Fishburne a Tony, Emmy, and SAG nomination for Best Actor.
