House Speaker Paul Ryan dismissed the protest as "nothing more than a publicity stunt." In an interview with CNN, he said the House will not vote on a "bill that takes away a person's due process."
Republicans emerging from a closed-door meeting said they would hold votes on other legislation, but not the gun votes demanded by the Democrats.
"We are going to go about our business starting tonight," said Rep. Ann Wagner, R-Mo. Democrats were certain to challenge any move.
The protest began around 11:30 a.m. By late afternoon, 168 House Democrats — out of 188 — and 34 Senate Democrats joined the protest, according to the House minority leader's office, and there was no sign of quitting.