BOISE, Idaho The Idaho Democratic Party wants federal election regulators to investigate whether Republican U.S. Senate candidate Jim Risch is improperly mixing campaign expenditures with those of his law office in his race against Democrat Larry LaRocco.

Campaign staffers for Risch, Idaho's lieutenant governor, disputed allegations of wrongdoing, saying their Federal Election Commission reports comply with election law, including monthly $2,500 payments for rent and services at campaign headquarters located in several rooms above Risch's law offices in Boise. Risch's law firm owns the building.

The Democratic Party wants to know, among other things, if Risch has adequately separated campaign costs from the law office's business; whether he's personally benefiting from rent payments to his office; and if payments for rent and services reflect their fair market value, according to a letter sent to the FEC on Wednesday.

"What we're trying to do is make the point that everyone has to follow the same set of rules," Chuck Oxley, the state Democratic Party's spokesman, said Thursday. "When the receptionist answers that campaign call, and puts the call through to Jim Risch, that's essentially a gift from the corporation."

Risch and LaRocco are vying to replace outgoing U.S. Sen. Larry Craig, a Republican who's not running again following his arrest in a gay sex sting last year in the Minneapolis airport.

Allegations the Risch campaign is inappropriately benefiting from mixing campaign activities with those of the law office are "baseless," according to the Risch campaign.

Jason Risch, Risch's son and a campaign spokesman, said the FEC reports filed by the campaign accurately reflect campaign expenditures and don't cross into office business. Campaign activities mostly occur in the upstairs rooms not occupied by the law offices, though occasionally a downstairs conference room may be used.

"We try very hard to keep things separate," said campaign manager Ryan White. "They've got their own organization downstairs, and obviously their own phone number. We don't run our phone system through them. We really don't do anything through them. We've even got our own entrance."

For the period from April 1 to June 30, Risch disclosed about $60,000 in rent- or staff-related payments, including $7,500 in total rent, at least $10,000 to campaign manager White and $13,000 to campaign treasurer John Insinger, one of Risch's law partners, for "legal and FEC compliance services."

LaRocco said the Democratic Party filed the complaint independently, but consulted with his campaign before sending the letter.

"We're confident our report is good, and we're interested in seeing what the FEC decides" about Risch's, said Dean Ferguson, a spokesman for LaRocco.

LaRocco, a former U.S. House member, has long chided Risch for what the Democrat says is fudging on election laws, including during the 2006 lieutenant governor run when he accused Risch of taking advantage of his seven-month stint as interim governor to use the state's turboprop airplane to fly around the state. Deputy Secretary of State Tim Hurst told The Associated Press on Thursday no formal complaint was lodged during the race two years ago. Risch beat LaRocco by nearly 19 percentage points.

FEC spokesman Bob Biersack said his agency hadn't received the Idaho Democratic Party's letter, signed by Jim Hansen, the executive director. Once it does, the Risch campaign would be given a chance to respond before FEC staff in Washington, D.C., even begin a review of the complaint's merit, Biersack said.

Resolution "can take many months, if it goes all the way through," he said.