The decision came after a Virginia Republican state legislator wrote a letter to university president Alan G. Merten protesting the Fairfax, Va., school's plans to pay the filmmaker $35,000 to speak on Oct. 28.
"We just felt it wasn't the most appropriate use of (public) funds, so we decided the best thing to do was cancel," school spokesman Daniel Walsch said.
George Mason, a state university, didn't notify Moore before making the decision public, Walsch said.
A message left seeking comment from Moore wasn't immediately returned to The Associated Press, but he told The Washington Post he plans to come and speak anyway.
"I'm going to show up in support of free speech and free expression," he said.
Loudoun County Del. Richard L. Black wrote a letter dated Tuesday urging Merten to reconsider the university's "lavish payment" to Moore, or to cancel the appearance.
"Tax money is being spent poorly, and for partisan purposes," wrote Black, who has one of the General Assembly's most conservative voting records.
Walsch said university officials didn't discuss with Moore whether they would allow him to speak if he waived his fee, nor did they approach student groups or other private organizations to come up with the money.
Moore's film, still playing in theaters, criticizes and ridicules President Bush's response to the Sept. 11, 2001, terrorist attacks and his decision to invade Iraq. It became the first documentary to top the $100 million mark, and its $118 million domestic total (as of early last month) was six times that of the previous record holder among feature-length documentaries, Moore's "Bowling for Columbine."
An alternately humorous and horrifying diatribe against President Bush and his actions regarding the Sept. 11 attacks, "Fahrenheit 9/11" blends Moore's cheeky wit with sobering images from Iraq and interviews with those affected by the war.
"We said from the get-go 'Fahrenheit' was not just informative but also broadly entertaining," said Tom Ortenberg, president of Lions Gate Films, one of the film's distributors. "We've always felt it was the combination of those two things that made it connect with audiences across the country."
Moore said he won't submit "Fahrenheit 9/11" for consideration as best documentary at this year's Academy Awards. Instead, he's going for the bigger prize of best picture.
"For me the real Oscar would be Bush's defeat on Nov. 2," Moore told The AP last month.
The George Mason controversy isn't Moore's first run-in with Republicans. When Monday about "a disingenuous film maker who would have us believe that Saddam's Iraq was an oasis of peace," they knew he was referring to the maker of "Fahrenheit 9/11."
McCain's comments prompted prolonged booing and chants of "Four more years." Many of the delegates faced Moore, who was seated in the press seats at Madison Square Garden because he was writing a column for USA Today.
, thrusting his arms over his head, laughing and saying, "Two more months."