Taxpayers trying to file their taxes online right at the deadline Tuesday were facing a major problem: The IRS site was not working.

David Kautter, the acting IRS commissioner, told House lawmakers that a number of the agency's systems were not working Tuesday.

"On my way over here this morning, I was told a number of IRS systems are unavailable at the moment," Kautter said during an appearance before the House Oversight Committee. "We are working to resolve this issues, and taxpayers should continue to file their returns as they normally would."

Kautter didn't go into more detail. But the IRS website said one particular function, the site's direct pay portal, was unavailable as of early afternoon.

Tuesday is Tax Day, an event that has taken on particular significance this year because of the enactment of the Republican tax overhaul package. On Capitol Hill, the law's advocates and critics planned events to mark the day. The House of Representatives planned to vote on IRS reform legislation later in the day.