The group of about 50 people took their protest to the halls of the Rayburn Building, which houses congressional offices, after a meeting with Rep. John Conyers, D-Mich., ImpeachBush.org said. Earlier, hundreds of people marched to the Capitol from Arlington National Cemetery to call for action against Bush and Vice President Dick Cheney.
Mara Verheyden-Hilliard, a spokeswoman for ImpeachBush.org, said Congress should act immediately to introduce articles of impeachment.
"Impeachment is not an option, it is a constitutional requirement," she said. "Representatives are mandated by their oath of office to carry out their constitutional duties."
Sheehan became one of the leading members of the anti-war movement after her son, Casey, was killed in Iraq.
While a number of Democrats in Congress also call for impeachment, House Speaker Nancy Pelosi and Majority Leader Harry Reid oppose it.