The US Supreme Court has heard arguments on a landmark case which could decide whether race can be used as a factor in university admissions.
The ultimate decision on the case is expected to be close
The case centres on three white students, two of whom were rejected from the University of Michigan and one who was turned down by the university's law school.
They say the decisions to reject them amounted to illegal discrimination by the university, and that if they had been a member of a minority group they would have been accepted.
The university has countered that race was only one factor in the process and that "affirmative action" - whereby students from ethnic minorities are given extra points during the admissions process - provides a more diverse student body of benefit to all races.
"This is one of the most important civil rights disputes to reach the court in the last quarter-century," American Civil Liberties Union representative Vincent Warren told Reuters news agency.
"At issue here is not only whether the University of Michigan can consider race in admissions, but also whether the doors to higher education will remain open to students of colour."
A large crowd of protesters supporting the university, including veteran civil rights activist Jesse Jackson, gathered outside the Supreme Court building on Tuesday, chanting and waving banners calling for support of affirmative action.
Former University of Michigan President Lee Bollinger told BBC News Online that "it would be a great pity" if the court rolled back 40 years of progress in racial diversity.
The case will be the most recent examination of US race relations since the court's decision in the Bakke versus Board of Regents case in 1978.
The case was brought by a white student, Allen Bakke, who argued he had been passed over by the University of California at Davis medical school in favour of minority candidates.
Court records show that if I had been black, Hispanic or Native American, I would have had a nearly 100% chance of admission with my grades and record
Rejected student Jennifer Gratz
In that instance, so-called "racial quotas" - whereby a certain number of places were set aside for minority candidates by the university - were struck down, but universities were still permitted to consider race as a factor in admissions.
The students have received the backing of several prominent conservative US figures, including President George W Bush who has taken a close interest in the case.
The US government's chief law officer, Solictor General Ted Olson, appeared in court to support the students' case and condemn the Michigan admissions plan as unconstitutional.
The US president has previously described affirmative action as still resembling "quota systems that... exclude people from higher education... are divisive, unfair and impossible to square with the Constitution".
However, support for the university has come from several civil liberties organisations and lawyers, including the American Bar Association.
Jennifer Gratz, one of the rejected students, said that she was rejected simply because of her skin colour.
"Court records show that if I had been black, Hispanic or Native American, I would have had a nearly 100% chance of admission with my grades and record."
However the ruling is expected to be close because of the ideological splits between the nine Supreme Court justices.
Analysts say that lawyers for both sides will be targeting the moderate conservatives for potential "swing" votes, with Justice Sandra Day O'Connor seen as the deciding vote.
A decision is expected in June.