Related: Supreme Court's affirmative action ruling prompts passionate reaction on both sides of issue

The U.S. Supreme Court upheld Michigan's controversial ban on affirmative action in public college admissions in a divided opinion released Tuesday morning, preserving a law that University of Michigan officials have said contributed to dwindling minority enrollment at the state's flagship college.

The high court's decision is a blow to diversity efforts at the U-M in Ann Arbor, which has come under fire for low minority enrollment.

Justice Anthony Kennedy wrote the majority opinion, Justice Sonia Sotomayor authored the dissenting opinion. The court's decision is divided 6-2, with justice Elena Kagan recusing herself from the case; she was the U.S. solicitor general when the case was before the lower courts.

Blacks comprise just 4.6 percent of undergraduates this year, compared to 8.9 percent in 1995 and 7 percent in 2006.

University of Michigan President Mary Sue Coleman and admissions director Ted Spencer have decried the affirmative action ban, saying outright that the school cannot achieve a fully diverse student body with it in place.

"It's impossible," Spencer said in a recent interview, "to achieve diversity on a regular basis if race cannot be used as one of many factors."

Fifty-eight percent of Michigan voters in 2006 passed Proposal 2, a ballot initiative that amended the state constitution and made it illegal for state entities to consider race in admissions and hiring. With the Supreme Court's ruling, the only way left to nullify Proposal 2 is to mount a long, expensive and uncertain campaign to overturn it.

The court heard oral arguments on Proposal 2 on Oct. 15, 2013, and a throng of Michigan and D.C.-area students rallied outside the court in support of affirmative action.

"With this ruling, there's really no effect on our policies, which are already consistent with Proposal 2," said U-M spokesman Rick Fitzgerald. "But we remain committed to the goal of a diverse student body and will continue to seek to reach that goal in ways that are consistent with the law."

By upholding Proposal 2, the high court bookends an era of contended affirmative action practices in Michigan, an epoch that began in 1996 when two students filed separate lawsuits against U-M questioning affirmative action practices in admissions.

In Grutter v. Bollinger, the Supreme Court upheld U-M Law School's limited use of race in admissions. In Gratz v. Bollinger the court struck down the undergraduate point-based admissions process, which awarded black applicants points based on race. The court decreed that although affirmative action was permissible the point system in place gave too much weight to race. Both cases were decided in 2003, and after revisions to admissions policies, U-M retained its use of affirmative action until the 2006 ban.

“Much progress has been made over the past 15 years in challenging discriminatory policies based on race preferences and moving toward colorblind government,” Jennifer Gratz, the plaintiff in the 2003 case Gratz v. Bollinger, said Tuesday morning. Gratz remains an outspoken opponent of affirmative action.

“Today’s ruling preserves this foundation and is a clear signal that states are moving in the right direction when they do away with policies that treat people differently based on race, gender, ethnicity or skin color," she continued.

Opponents of Proposal 2 mounted a lawsuit against the higher education piece of the ban almost immediately after it was passed.

Demonstrators arrive at the Supreme Court after marching from the Lincoln Memorial to rally for affirmative action and against Michigan's Proposal 2 on Oct. 15, 2013.

The group By Any Means Necessary argued that the ban violated the equal protection provision in the 14th amendment of the U.S. Constitution. The group argued that to get a school to consider race, someone would have to overturn an amendment to the state constitution; whereas, to get a school to consider other factors, such as legacy or socioeconomic status, someone just has to lobby a governing board.

In his opinion, Justice Kennedy disagreed with BAMN's determination.

"This case is not about how the debate about racial preferences should be resolved. It is about who may resolve it," he wrote. "There is no authority in the Constitution of the United States or in this Court’s precedents for the Judiciary to set aside Michigan laws that commit this policy determination to the voters."

He continued: "Deliberative debate on sensitive issues such as racial preferences all too often may shade into rancor. But that does not justify removing certain court-determined issues from the voters’ reach."

Michigan attorney general Bill Schuette's office has been a fierce defender of Proposal 2, and initially a federal judge in Detroit upheld the ban.

Yet a three-judge panel of the Sixth Circuit Court found it unconstitutional, and then the full slate of judges in the Sixth Circuit, in an 8-7 opinion, backed the panel's decision in November 2012.

The Sixth Circuit's decision conflicted with another appeals court, the Ninth Circuit on the West Coast, which had upheld California's ban on affirmative action in an earlier case. The Supreme Court agreed to hear the Michigan case and settle the conflicting opinions.

“It is curious to say that a law that bars a state from discriminating on the basis of race or sex violates the Equal Protection Clause by discriminating on the basis of race," his office wrote in a brief filed with the Supreme Court.

The Supreme Court's decision overturns the Sixth Circuit's decision, a ruling many who watch the court closely had expected.

The ruling effectively upholds similar bans in five other states: Arizona, Nebraska, Oklahoma, California and Washington

California passed its ban on affirmative action in 1996, and the state's public schools have since experienced low minority enrollment. In 2010, 3.4 percent students in the University of California system were black and 5.2 percent of students in the California State University system were black.

Mark Rosenbaum is an attorney with the American Civil Liberties Union who argued before the Supreme Court in October in defense of affirmative action, and against the ban. In his view, the Supreme Court's decision will make it difficult for schools in Michigan and other states with affirmative action bans in place — including Arizona, Nebraska, Oklahoma, California and Washington — to achieve a racially diverse student body.

"It's profoundly disappointing. The big losers are the citizens and the students of the state of Michigan," he said."It's going to put true educational diversity out of reach and permit preferences on behalf of children of donors, alumni, athletes, but keep raciai identity as if it doesn't exist."

Meanwhile, at U-M the Black Student Union and other student groups have condemned low minority enrollment at the school and demanded 10 percent black representation on campus. The demand is a leap from the existing 4.6 percent black enrollment, but it is in line with promises the university made to black students in the 1970s.

Proposal 2 limits not only how U-M can consider an applicant's file, but also how the school can offer financial aid packages and scholarships. The school can't target aid to specific races, a restriction admissions director Spencer says is the most damaging of all.

Kellie Woodhouse covers higher education for the Ann Arbor News. Reach her at kelliewoodhouse@mlive.com or 734-255-5303 and follow her on twitter.