Affirmative action has always been a controversial topic, with Americans split nearly down the middle on whether or not such policies should be enforced.

Conservative Supreme Court justices on Monday expressed skepticism about the lawfulness of affirmative action in college admissions as they weighed cases challenging policies at the University of North Carolina and Harvard University.

Members of the court’s conservative wing questioned the legal rationale for allowing the consideration of race and probed to what extent universities could enact new “race neutral” admissions policies aimed at improving racial diversity.

Liberal justices in the minority defended the use of race in admissions, citing the importance of diversity on campus and the difficulty of achieving that goal without any consideration of race.

Affirmative action, introduced to redress historic discrimination, has been a contentious issue for years, strongly supported by educational institutions and corporate America as vital to fostering diversity and condemned by conservatives as antithetical to the notion that racial equality means that all races are treated the same.

The Supreme Court, which has a 6-3 conservative majority, is hearing back-to-back oral arguments in the UNC and Harvard cases; the session is likely to last several hours. The arguments against affirmative action are being brought by a group called Students for Fair Admissions, led by conservative activist Ed Blum.

Justice Samuel Alito pushed back against the whole notion of applicants disclosing their race in applications.

“What do you learn from them checking a box?” he asked UNC lawyer Ryan Park.

Conservative justices appeared skeptical that universities would ever conclude that their diversity targets have been met, coming into conflict with the Supreme Court’s own 2003 ruling that said affirmative action would no longer be needed after 25 years.

“I don’t see how you can say that the program will ever end,” Roberts told Park.

Conservative Justice Clarence Thomas questioned whether universities have a compelling interest in diversity, while fellow conservative Justice Neil Gorsuch expressed concern that the goal of achieving diversity was akin to having racial quotas, which the court has previously prohibited.

Several conservatives, including Chief Justice John Roberts and Justice Brett Kavanaugh, probed whether, if race could not be considered, universities could enact race-neutral policies that were intended to lead to more racial diversity, a major potential follow-on issue were the court to end affirmative action. The fact that justices were asking about it suggests they are anticipating that explicit consideration of race could be be ended.

As affirmative action supporters rallied outside the courthouse, the first oral argument on UNC’s policy began with liberal Justice Sonia Sotomayor questioning the challengers’ lawyer, Patrick Strawbridge, on how college administrators can assess applicants from diverse socio-economic backgrounds without considering race.

“Sometimes race does correlate to some experiences and not others,” Sotomayor said. “If you are Black, you are more likely to be in an under-resourced school. You are more likely to be taught by teachers who are not as qualified as others. You are more likely to be viewed as having less academic potential.”

Liberal Justice Ketanji Brown Jackson pushed back on Strawbridge’s description of UNC’s process, saying race is never considered alone.

“You haven’t demonstrated or shown one situation in which all they look at is race and take from that stereotypes and other things. They are looking at the full person,” she said.

The university is not solely considering race “just because somebody checks a box,” she added.

Jackson also questioned whether ending consideration of race would create new legal issues. She wondered, for example, whether it would be discriminatory if Black students descended from slaves were not allowed to speak about their family backgrounds on their applications but white students from North Carolina still were able to discuss theirs.

Liberal Justice Elena Kagan, the former dean of Harvard Law School, strongly defended the value of racial diversity on campus, saying that colleges are “pipelines to leadership in our society.”

The group’s lawyers have asked the justices to overturn the2003 ruling, Grutter v. Bollinger, in which the court said race could be considered as a factor in the admissions process because universities had a compelling interest in maintaining a diverse campus. The legal debate was left unresolved by a fractured 1978 Supreme Court ruling in which the justices prohibited racial quotas but left the door open to some consideration of race.

In 2016, the last time the Supreme Court ruled on affirmative action, the justices narrowly upheld the admissions policy at the University of Texas at Austin on a 4-3 vote with conservative Justice Anthony Kennedy, who has since retired, casting the deciding vote.

The court shifted to the right following former President Donald Trump’s appointment of three conservative justices. President Joe Biden’s appointment of Jackson did not change the ideological balance of the bench, as she replaced fellow liberal Justice Stephen Breyer. As Jackson previously served on Harvard’s board of overseers, she has stepped aside from that case and will only participate in the North Carolina dispute.

Blum’s group argues that any consideration of race in university admissions is unlawful under both federal law that bars discrimination in education and the equal protection clause of the 14th Amendment to the Constitution. They argue that the UNC admissions policy discriminates against white and Asian applicants and that the Harvard policy discriminates against Asians. In both cases, lower courts ruled in favor of the universities.

In defending their policies, the universities and their supporters — including the Biden administration, civil rights groups, businesses and former military leaders — argue that excluding someone based on race is completely different to seeking diversity on campus. The universities say race is just one factor that is considered as part of broad individualized analysis of each applicant.

If affirmative action is ended, those defending the practice say, race-neutral policies aimed at achieving diversity will often fail, leading to a decline in Black and Hispanic enrollment. The challengers point to examples in the nine states that already ban the practice as evidence that consideration of race is not essential.