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 ordinance division were called to the organization’s D.C. offices. 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.

Police are also investigating a suspicious package found at the Canadian Embassy in Washington.

Reporter Matt Boyle contributed to this report.