Staffers at Americans for Tax Reform, the anti-tax group run by conservative activist Grover Norquist, evacuated their building Monday morning after a bomb threat was called in, according to authorities.

A spokesman for the Washington D.C. police department, Anthony Clay, confirmed to The Daily Caller that officers from the explosive ordnance division were called to the building that houses the organization’s D.C. offices shortly after 9 a.m.

The employees have since been allowed to return to work, another officer told TheDC from the scene.

No explosives were found, the officer said. Police had shut down 12th Street in Washington near ATR’s offices.

“The police are conducting an investigation,” said John Kartch, a spokesman for ATR, in an email.

Norquist and his group’s Taxpayer Protection Pledge have been in the news with Congress wrestling over raising the country’s debt limit. The ATR pledge is a commitment by candidates and elected officials that they will oppose and vote against any tax increases.

It has come into focus as the Democrats push for revenue increases as part of a deficit reduction package. Norquist has had to defend the pledge from people who say it “gets in the way of a deal to allow a debt ceiling increase,” he wrote in the New York Times last week.

Also in D.C on Monday, police investigated a suspicious package found at the Canadian Embassy.

Reporter Matt Boyle contributed to this report.