After the Supreme Court ruled a decade ago that race could be a factor in college admissions in a Michigan case, affirmative action opponents persuaded the state's voters to outlaw any consideration of race.

Now, the high court is weighing whether that change to Michigan's constitution is itself discriminatory.

It is a proposition that even the lawyer for civil rights groups in favor of affirmative action acknowledges a tough sell, at first glance.

"How can a provision that is designed to end discrimination in fact discriminate?" said Mark Rosenbaum of the American Civil Liberties Union. Yet that is the difficult argument Rosenbaum will make on Tuesday to a court that has grown more skeptical about taking race into account in education since its Michigan decision in 2003.

A victory for Rosenbaum's side would imperil similar voter-approved initiatives that banned affirmative action in education in California and Washington state. A few other states have adopted laws or issued executive orders to bar race-conscious admissions policies.