The U.S. Supreme Court rejected a bid Monday from the Academy of Art University in San Francisco that could have halted a decadelong case by former employees who say the school cheated the government out of millions of dollars in student loans and grants.

By declining to take the case, the high court let stand a Ninth U.S. Circuit Court of Appeals ruling from August that said it can go forward because evidence exists that the huge for-profit art school may have used illegal tactics to enroll students from 2006 to 2010.

The 90-year-old Academy of Art is one of the nation’s largest art schools with 13,000 students — many of them taking courses online, according to a report last year by its accreditor, the Western Association of Schools and Colleges’ Senior College and University Commission. It also is one of the city’s largest property owners.

The Supreme Court’s rejection marks the fifth time since 2009 that the school has tried and failed to get the case tossed out. Its only remaining options are to settle or go to trial.

Either way could be expensive for the school.

The former employees — Scott Rose, Mary Aquino, Mitchell Nelson and Lucy Stearns — are suing under the federal False Claims Act, which awards triple damages to encourage whistle-blowers to come forward if they believe the government is being cheated. They have said their suit could cost the school $450 million. Whatever the damages, 70 percent would go to the federal government. The plaintiffs and their lawyers could keep the rest.

The four sued the Academy of Art in federal court in 2009, saying the school dangled raises of up to $30,000 and trips to Hawaii based on the number of students they recruited. The ex-recruiters called it an “incentive compensation” scheme of a kind banned by the federal government to prevent colleges from enrolling unqualified applicants who are unlikely to graduate or pay back their government-backed student loans. At the same time, they told the court, the art school reduced their pay when they missed recruitment goals.

Since 2006, the Academy of Art has collected more than $1.5 billion in federal student loans and at least $171 million in Pell and other federal grants, according to a Chronicle analysis of federal records.

The former recruiters claim these millions of dollars motivated the school to vigorously court growing numbers of students at all cost.

The Academy of Art has told the court it did nothing illegal, and that the recruitment incentives it used at the time were allowed under a federal “safe harbor” provision created by the Bush administration in 2002 and rescinded by the Obama administration in 2010.

The school’s attorney, Steve Gombos, declined Monday to comment on the case or on the high court rejection.

The plaintiff’s attorney, Stephen Jaffe, said his clients “look forward to pursuing a fair resolution of the lawsuit.”

The case now goes back to the U.S. District Court in Oakland. It could still take months before a trial date is set, during which both sides are expected to continue settlement talks.

Meanwhile, the Academy of Art continues enrolling students. Its website lists annual tuition and fees at about $25,000, with prices rising to more than $26,000 for next fall. Student housing, in 15 buildings the school leases from its owner, Elisa Stephens, costs $8,200 to $16,400 a year.

Stephens, 60, is a society figure known for lending classic cars to civic and charity functions, while pedestrians can see her Bugattis, Duesenbergs and other roadsters through the windows of a showroom on Van Ness Avenue. The university owns 40 buildings across the city, many of which were out of compliance for years with San Francisco planning codes.

Ultimately, City Attorney Dennis Herrera sued the Academy of Art over the properties and settled in 2016 for $60 million.

Nanette Asimov is a San Francisco Chronicle staff writer. Email: nasimov@sfchronicle.com Twitter: @NanetteAsimov