The Supreme Court in a pair of cases Thursday severely limited the use of race as a factor in college admissions, upending decades of affirmative action programs that U.S. institutions have used to select students from their applicant pools.

In rulings that broke along ideological lines, the court’s six conservative justices invalidated Harvard’s and University of North Carolina at Chapel Hill’s (UNC) admissions practices by ruling they did not comply with the 14th Amendment’s guarantee of equal protection.

“Both programs lack sufficiently focused and measurable objectives warranting the use of race, unavoidably employ race in a negative manner, involve racial stereotyping, and lack meaningful end points,” Chief Justice John Roberts wrote for the majority. 

“We have never permitted admissions programs to work in that way, and we will not do so today,” he continued. “At the same time, as all parties agree, nothing in this opinion should be construed as prohibiting universities from considering an applicant’s discussion of how race affected his or her life, be it through discrimination, inspiration, or otherwise.”

In a rare occurrence, conservative Justice Clarence Thomas read his concurring opinion from the bench, advocating for a colorblind view of the Constitution. Liberal Justice Sonia Sotomayor also read her dissent.

“The Court today makes clear that, in the future, universities wishing to discriminate based on race in admissions must articulate and justify a compelling and measurable state interest based on concrete evidence. Given the strictures set out by the Court, I highly doubt any will be able to do so,” Thomas wrote.

The court’s decision adds to a legal crusade by conservative legal strategist Edward Blum, who formed Students for Fair Admissions (SFFA) and separately challenged the admission policies of Harvard and UNC nearly a decade ago.

The Biden administration had backed the two schools before the justices. But after affirmative action at colleges survived multiple previous challenges at the Supreme Court, the bench’s increasingly conservative makeup has now handed down a major blow.

“In other words, the student must be treated based on his or her experiences as an individual—not on the basis of race,” Roberts wrote. “Many universities have for too long done just the opposite. And in doing so, they have concluded, wrongly, that the touchstone of an individual’s identity is not challenges bested, skills built, or lessons learned but the color of their skin. Our constitutional history does not tolerate that choice.”

After Justice Ketanji Brown Jackson joined the bench last year, the justices considered SFFA’s challenges separately; Jackson served on Harvard’s Board of Overseers until last spring and agreed to recuse herself from that school’s case during her confirmation hearing.

The court handed down a 6-3 ruling against UNC and a 6-2 ruling against Harvard, given Jackson’s recusal in the latter.

The Supreme Court first laid the groundwork for affirmative action in 1978 as it decided a challenge to the University of California’s system that reserved 16 out of 100 seats for members of certain minority groups. 

The justices in a splintered decision struck down the quota system, but no opinion garnered a majority of votes. Lower courts were left grappling with whether to consider as binding precedent the opinion of Justice Lewis Powell, whose swing vote invalidated the quota while more broadly upholding race-conscious admissions.

Schools across the country modeled their affirmative action programs on Powell’s opinion in the years following.

“Today, this Court stands in the way and rolls back decades of precedent and momentous progress,” Sotomayor wrote in dissent. “It holds that race can no longer be used in a limited way in college admissions to achieve such critical benefits. In so holding, the Court cements a superficial rule of colorblindness as a constitutional principle in an endemically segregated society where race has always mattered and continues to matter.”

A quarter-century later, a majority of justices in Grutter v. Bollinger upheld affirmative action by endorsing Powell’s argument. They ruled Title VI and the Equal Protection Clause allowed the narrowly tailored use of race in admissions decisions to further a compelling interest in obtaining the educational benefits that flow from a diverse student body.

The Supreme Court left affirmative action intact in two subsequent challenges.

In a 2013 case challenging race-conscious admissions at the University of Texas at Austin, the justices sent the case back to a lower court after finding it did not apply Grutter correctly. Three years later, the case returned to the Supreme Court, and the school emerged victorious.

In all three instances, Republican-nominated justices authored the majority opinions. In Grutter, however, Justice Sandra Day O’Connor wrote for the majority that they expected the use of racial preferences “will no longer be necessary” in 25 years.

Her decision marked its 20-year anniversary June 23.

Updated 10:52 a.m. ET.