The campaign is looking into hundreds of thousands of dollars in contributions to make sure that they are appropriate, a spokesman said.
The campaign sent a letter spelling out legal requirements to all donors who sent their contributions through Harry Sargeant III, the finance chairman of the Florida Republican Party.
It's illegal for foreigners to contribute their own money to U.S. campaigns.
The New York Times reported Thursday that Sargeant allowed a longtime business partner, Mustafa Abu Naba'a, to bring in some $50,000 in donations in March from members of a single extended family, the Abdullahs, in California, along with several of their friends.
A House committee chairman is looking into Sargeant's defense contracts for shipping fuel to U.S. bases in Iraq as part of a probe into whether contractors are engaging in overcharging.
McCain spokesman Brian Rogers said Mustafa Abu Naba'a is not a bundler for the campaign, although Sargeant is.
"He wasn't registered, and he hasn't contributed," Rogers said of Mustafa Abu Naba'a.
The campaign letter to donors notes that federal law bars contributions from foreign nationals and that donations cannot be reimbursed.
Eight months ago, a top fundraiser for Hillary Clinton, Norman Hsu, was indicted for making contributions to various political candidates in the names of others.
McCain is co-sponsor of the campaign finance reform law that bears his name and he is trying to resolve any questions involving Sargeant.
McCain has "a deep commitment" to strictly following campaign finance law, said Rogers.
According to The Times, Abu Naba'a is a dual citizen of Jordan and the Dominican Republic.
Federal election regulations bar foreign nationals from participating in campaign decision-making involving donations.
Regarding donations from the extended Abdullah family in California, some couples contributed thousands of dollars to Clinton, a Democrat, and Rudolph W. Giuliani, a Republican. Other Arab-Americans in California contributed thousands to a longtime friend of Sargeant, Florida Gov. Charlie Crist, a Republican.