In what are becoming heated exchanges over ethics in Virginia’s 10th Congressional District race, Republicans on Tuesday attacked Fairfax County Supervisor John W. Foust for filming a commercial inside the county government center.

County and state officials said there was nothing out of the ordinary in using the government building for a commercial about cutting government waste that began airing Tuesday, a 31-second spot for which the Democrat’s campaign obtained a permit earlier this month.

But after a journalist called the location “unusual” in a tweet, supporters of Foust’s Republican opponent, Barbara J. Comstock, noted that Fairfax ethics guidelines prohibit employees and elected officials from using any county facilities for political purposes.

County regulations governing Fairfax properties say the government center complex can be used by employees only for official county business or “personal/private use.”

“It’s troubling that John Foust would use government facilities, which are paid for by taxpayers, to film his political commercials,” said Katie Prill, spokeswoman for the National Republican Congressional Committee, noting Foust’s name is not on the permit. “This is clearly outlawed by Fairfax County’s own code of ethics and personnel regulations, but apparently Foust thinks he’s above the rules.”

Foust’s campaign manager called the charge “ludicrous.”

“I would not have filmed there if it wasn’t permitted,” said Shaun Daniels, the campaign manager.

A spokeswoman for Comstock declined to comment, other than to call the commercial “laughable” in its depiction of Foust as a diligent cutter of government waste.

The Fairfax County government center is listed as an approved site for filming by the Virginia Film Office.

Dawn Blacksten, a project manager for state film office, said government buildings are frequently used as sites for political commercials.

For instance, “In the last senator’s race, I think everyone filmed inside the state capitol,” she said.

Fairfax County spokesman Tony Castrilli said the rules governing political activity inside government buildings do not apply to filming commercials.

But in a congressional race that both major parties see as crucial to gaining leverage in Congress, every score with voters is crucial.

Last week, the Foust campaign lambasted Comstock after The Washington Post reported that her campaign failed to disclose $85,000 earned in 2012 by one of her companies — an oversight her campaign said was inadvertent and quickly corrected.

“Barbara Comstock’s failed attempt to hide her clients is a shocking and disturbing breach of trust,” Foust said earlier this week in a statement.