FAIRFAX, Va. (AP) — George Mason University, a public school outside the nation's capital, has quietly become a conservative powerhouse in economics and law, a reputation built in part with tens of millions of dollars a year from billionaire Republican donor Charles Koch.

From 2011 to 2014, the Charles Koch Foundation gave nearly $48 million to George Mason in one form or another, tax records show. Though Koch divvies up more than $20 million annually among hundreds of U.S. universities through his foundation, no other school got more than $1 million annually in that period.

Although it is not unusual for billionaires — including those on the other end of the political spectrum — to donate large sums to schools, the size of the donations has raised concerns among some George Mason students and faculty about maintaining academic independence, echoing unease that has cropped up at other schools that benefit from Koch's largesse.

Other billionaires have made larger lump-sum contributions to schools, typically for a specific purpose such as a research facility. Earlier this year, Nike Inc. co-founder Phil Knight, who also supports Republican causes, announced a $400 million scholarship donation to Stanford University.

And Koch and his younger brother David have themselves made bigger one-time donations to other universities.

Charles Koch's representatives say the generosity comes without conditions. Supporters say the money fills a gap left by declining public support and accuse critics of targeting Koch, CEO of the petrochemical conglomerate Koch Industries Inc., because of his outspoken backing of conservative and libertarian causes.

Koch's giving has tripped alarms at George Mason, where boards and institutes are peppered with people with close ties to Koch Industries.

In 2014, the last year for which records are available, the foundation gave $16.8 million to George Mason and its Institute for Humane Studies. That accounts for more than a third of the money GMU gets from private sources: The Council for Aid to Education, a not-for-profit organization that drives corporate giving to colleges, reports Mason received $44.6 million in donations in fiscal 2013.

And the relationship continues to grow: on Thursday, Mason's law school announced a $10 million gift from the Koch Foundation, along with $20 million from an anonymous donor, to rename the law school for the late conservative Supreme Court Justice Antonin Scalia. GMU President Angel Cabrear called the donations "a milestone moment for the university."

Thursday's gift to the law school aside, George Mason has steered the bulk of the money to its Mercatus Center, a free-market think tank that conducts research designed to educate the federal regulators and congressional staffers whose work on arcane, wonky policy can influence the direction of government.

The other large chunk of Koch funds goes to the Institute for Humane Studies, which advocates libertarian philosophies. Its Learn Liberty project produces and distributes videos opposing minimum wage hikes and questioning efforts to combat wealth inequality.

Why George Mason? The school's growth since its founding in 1972 has coincided with Koch's growing philanthropy. George Mason has longstanding connections with the Kochs, notably Richard Fink, an executive vice president of Koch Industries who is on the Mercatus and IHS boards.

On the university's board is Kimberly Dennis, president and CEO of the Searle Freedom Trust, a grant-making foundation with close ties to the Kochs. Before her, Nancy Pfotenhauer, a former spokeswoman for Republican Sen. John McCain's presidential campaign and the head of Koch Industries' Washington office, was on the board.

And Charles Koch himself is chairman of the IHS board and a member of the Mercatus board.

Cabrera said Koch's status as a lightning rod for his support of Republican candidates is the only reason people question his donations, and said he welcomes Koch's active interest in how money is spent.

"It's terrific to have people who are supportive not only with their dollars, but also with some of their time," Cabrera said. "I make no apologies about that. I celebrate that."

Koch critics say there is a difference between wealthy donors contributing to their alma maters — Knight went to Stanford's business school, for instance — and Koch's effort to establish himself at hundreds of universities across the nation.

They cite the agreement that first brought the Mercatus Center to George Mason in 1992, which allowed the center to hire two tenure-track professors of its choosing, with the understanding the university would eventually assume responsibility for the professors' salaries.

In 2013, the Koch Foundation signed an agreement to create a Program for the Study of Political Economy and Free Enterprise at Florida State University. The agreement gave Florida State authority to hire professors, but required that the professors support the program's objectives, spelled out as advocating a libertarian philosophy "to advance the understanding and practice of those free voluntary processes and principles that promote social progress, human well-being, individual freedom, opportunity and prosperity."

Florida State was criticized for ceding academic control to the Kochs, but the Koch Foundation's director of university relations, John Hardin, said the accusations are not supported by the actual agreements that the foundation has entered into. He said the donations to Florida State, George Mason and other schools come with no strings attached.

"We recognize our role is to write the checks," Hardin said.

The foundation's support for criminal justice reform has brought it together with the American Civil Liberties Union and other organizations often perceived on opposite sides of the ideological spectrum, he said.

Martin Kich, an English professor at Wright State University who has written critically of the Kochs' influence in higher education, said he sees that influence as part of a larger trend of university administrators willing to accept money with strings attached.

"To reduce this to a left-right political (battle) is missing the point," he said.

For four years, a faculty senate committee has explored Koch's relationship with George Mason, but said it has been stymied by the school's refusal to turn over details of the grant agreements with the Koch Foundation.

Dave Kuebrich, an English professor who heads the committee, said he does not believe the agreements restrict academic freedom but that he suspects the decades-long relationship makes such overt restrictions unnecessary.

The university needs to establish better principle to protect academic independence and avoid conflicts of interest, Kuebrich said, emphasizing that he wasn't speaking for the committee.

"That's not unique to George Mason, by the way," he said. "What might be unique is that we have these centers clustered so close to the nation's capital that are trying to build a movement to influence public policy."

Students Samantha Parsons and Colin Nackerman have been leading an effort demanding the university explain its relationship with Koch. They started petition drives and bird-dogged Cabrera at public appearances, but their request to meet with him has not been fulfilled.

In academic circles, the school's law and economics programs have clear reputations as libertarian strongholds.

"It is one of the most ideologically homogenous law schools in the nation. And the ideology is 'the market is always right; get the government out of it,'" said Brian Leiter, the director of the University of Chicago's Center for Law, Philosophy and Human Values, who conducts research on law schools' scholarship.

Though the Koch grant bars Mercatus from using the money to influence legislation, the center prides itself on conducting research that migrates from the ivory tower into the real world and onto Capitol Hill. Its senior researchers regularly testify to Congress supporting measures to reduce regulation and market intervention.

A 2004 Wall Street Journal article called Mercatus — Latin for "markets" — the "most important think tank you've never heard of," citing its uncanny ability to inject its policy recommendations into the national political conversation.

While Democrats nationally have railed against Koch's political influence, Virginia Democrats don't seem riled by the donations to George Mason.

Democratic Sen. Chap Petersen, whose district includes the university's main campus in Fairfax, said that regardless of its origins, the money helps fill a funding gap.

"Does it bother me that the Kochs are funding George Mason University to further their intellectual policy goals?" he asked. "No, it does not bother me."