U.S. Rep. Chris Gibson, R-Kinderhook, worked an hour past midnight Wednesday and was back up at 6 a.m. Thursday to start work again, said his spokeswoman Stephanie Valle.

"It's a busy week down here, so he's got an incredible amount of work to do," she said.

The five hours of sleep the congressman got were on an air mattress he stores in his office to sleep on nights that he is in Washington.

Some say Gibson is being frugal, by sleeping in his office instead of renting an apartment or hotel room.

But a Washington, D.C.-based advocacy group says Gibson and about 30 other congressman who routinely sleep in their offices are receiving a taxable benefit that lawmakers should be reporting to the IRS.

The group Citizens for Responsibility and Ethics in Washington on Thursday asked the Office of Congressional Ethics to investigate whether lawmakers who sleep in their offices are breaking congressional rules and getting an unfair tax break by making personal use of public facilities.

The practice is nothing new. Lawmakers for years slept on Capitol Hill to avoid paying expensive rents.

But the group says House rules prohibit using taxpayer resources for anything but official purposes.