In a statement, House Speaker John Boehner, R-Ohio, said the House would not convene at 10 a.m. EDT for morning business, but lawmakers were expected to convene at noon to begin legislative work. The Senate still planned to go into session as scheduled at 10 a.m. EDT.
A hazardous material response team was on site following an incident that began sometime around 2:30 a.m. to 3 a.m., Capitol Police said.
Entry to the House side of the Capitol was temporarily closed but later opened. The East Grand staircase from floors one to three and one room on the third floor remained closed.
Tours of the Capitol building resumed as the visitor center was not affected. The House Press Gallery was reopened later in the morning.
The Architect of the Capitol released a statement indicating the incident involves possible asbestos exposure.
"During ongoing asbestos abatement work there was a potential release affecting the House side of the Capitol," the statement read. "Samples have been collected to determine whether there was potential exposure."