The U.S. Supreme Court is taking up a challenge to a University of Texas program that considers race in some college admissions. The case could produce new limits on affirmative action at universities, or roll it back entirely.

The university says the program that fills roughly a quarter of its incoming classes uses race among many factors and argues that is necessary to provide the kind of diverse educational experience the high court has previously endorsed. The rest of its slots go to students who are admitted based on their class rank, without regard to race.

Opponents of the program say the university is practicing illegal discrimination by considering race at all.

Justice Elena Kagan is not taking part, probably because she worked on the case at the Justice Department.