Two days after they missed their swearing-in on the House floor, Reps. Mike Fitzpatrick of Bucks County and Pete Sessions of Texas apologized Friday for the blunder.

In a letter addressed to the newly elected speaker, fellow Republican John Boehner of Ohio, the men said they regretted any inconvenience the misstep caused.

"We are deeply committed to fulfilling our role in our constitutional democracy by maintaining the integrity of the People's House," read their letter, which they made public. "Our absence on the House floor during the oath-of-office ceremony for the 112th Congress - while not intentional - fell short of this standard by creating uncertainty regarding our standing in this body."

In an interview late Friday, Fitzpatrick defended the Wednesday-afternoon reception that distracted him from his swearing-in duty, saying it was in no way, shape, or form a campaign fund-raiser, as Democrats have alleged.

House ethics officials "gave us very specific instructions that campaign funds could be used for that purpose," Fitzpatrick said. "The reception was open to anybody. . . . There was no charge. It was not a fund-raiser, and it is quite a stretch to suggest otherwise."

But on a day when Democrats and two nonpartisan watchdog groups called for an ethics probe into the matter, some experts said the reception, held on federal grounds, could be a problem.

Fitzpatrick and Sessions were visiting with more than 500 Fitzpatrick supporters at the Capitol Visitor Center when Boehner administered the oath on the House floor. Both men raised their hands and recited the oath as they watched Boehner on live television.

House parliamentarians decided that wasn't good enough and recommended that the pair be officially sworn in. Boehner did so Thursday, and on Friday, the House nullified a half-dozen votes Fitzpatrick and Sessions cast before the second ceremony.

Many House members used campaign funds to underwrite receptions this week - a method that House rules encourage, as a guard against illegal use of federal money for such events.

The Fitzpatrick campaign's invitation to the Washington event solicited contributions. That could run afoul of House ethics rules, said Stanley Brand, who served as general counsel to the House from 1976 to 1983, when it was under Democratic control. He said such a breach would be minor.

"That would generally be a prohibited transaction," Brand said Friday in an interview. "You would not generally be allowed to use official space in the House for soliciting campaign contributions."

Fitzpatrick said some attendees at his reception paid $30 apiece to cover the cost of a bus ride to Washington, but no other funds were raised.

The invitation allowed for larger contributions and asked those donating by check to send money directly to Fitzpatrick's campaign fund.

"It's activity related to fund-raising, whether or not somebody handed a dollar over to him at the time," said Craig Holman, an ethics expert and lobbyist with the nonpartisan group Public Citizen. "No member of Congress nor their staff is supposed to be doing fund-raising in the Capitol or using any sort of official resources. . . . It sounds like it is a direct violation."

Brand said the invitation should have spelled out that any funds raised went toward transportation costs only and that donations would not be accepted in exchange for attending a reception on federal property.

But the veteran Washington lawyer said that if there was a violation, it was small.

"Look, there's a difference between unethical conduct and illegal conduct, criminal conduct and foolish conduct," Brand said. "The better part of discretion is to not invite this kind of scrutiny."

Jon Steinman, spokesman for the Office of Congressional Ethics, declined to comment on whether that office, formed in 2008, would look into the reception.

Two groups in Washington, the Sunlight Foundation and the Campaign Legal Center, called for an investigation. Such a probe could produce a report to the House Ethics Committee, which could determine if any penalty was warranted.

"On this," Holman said, "I would expect the Ethics Committee to hand out probably a private letter of reprimand."

Fitzpatrick, 47, of Middletown Township, served a term in the House before he was defeated by Democrat Patrick Murphy in 2006. He won his seat back from Murphy last fall.

Fitzpatrick said Friday that he had planned to be in the House for the swearing-in, but that the day's schedule was fluid and he wanted to show respect to those who came from Bucks County to cheer him.

"I feel very badly about that," he said. "The administration of the oath is an important occasion, and I intended to be on the floor."