Dozens of Democrats pushing for action on gun control protested on the floor of the House of Representatives, chanting "No bill, no break!" and demanding that the chamber put off an upcoming recess until legislation is debated.
The protest was the latest move by Democrats to persuade the Republican majority in Congress to take up gun control in response to last week's mass shooting in Orlando, Florida, which has been described as one of the deadliest in modern US history.
The Democrats stood or sat at the front of the chamber, where such tactics are relatively rare.
When the presiding House officer, Republican Representative Ted Poe, entered the chamber, he declared the House not in order.
After banging the gavel several times in an attempt to clear the protesters, he announced the chamber would be in recess and left.
The Democrats remained on the House floor, calling for action before a vacation recess scheduled to start at the end of the week and run till July 5.
Assistant Democratic Leader James Clyburn likened the push for gun control action to the civil rights movement of the 1960s, when sit-ins and other civil disobedience prodded Washington to act on new protections for African-Americans.
Democratic presidential candidate Hillary Clinton tweeted her support for the sit-in, saying: "This is what real leadership looks like."
Democrats in the Senate last week took control of that chamber for nearly 15 straight hours as they called for gun control legislation.
On Monday, the Senate failed to advance four gun measures, including one that would have prohibited gun sales to people on a broad range of government watch lists.
Senators from both parties now are pushing for a compromise. Senate Majority Leader Mitch McConnell said he would schedule a vote on the measure by fellow Republican Senator Susan Collins that would prevent about 109,000 people on "no-fly" and other surveillance lists from purchasing guns.