The White House announced a crackdown on firearms sales at gun shows and over the internet that evade US federal background checks.
Vice President Kamala Harris, who heads the White House Office on Gun Violence Prevention, told reporters the move addresses the so-called "gun show loophole."
"Currently, gun stores are required by law to conduct a background check for every gun sale," Harris said.
"But for decades, many dealers who sell weapons someplace other than the traditional gun store... have gotten away without conducting background checks," she said.
"All gun dealers now must conduct background checks, no matter where or how they sell their merchandise."
Gun violence is common in the United States, a country where there are more firearms than people. Attempts to clamp down on gun rights are always met with stiff political resistance.
Harris said thousands of unlicensed dealers sell tens of thousands of guns a year without conducting background checks.
Among those who have been able to purchase firearms through the "gun show loophole" are domestic abusers and violent felons, she said.
"Under this regulation, it will not matter if guns are sold on the internet, at a gun show, or at a brick-and-mortar store," Attorney General Merrick Garland said in a statement.
"If you sell guns predominantly to earn a profit, you must be licensed, and you must conduct background checks," Garland said.
A senior White House official said the Biden administration expects the move will be challenged in court by gun rights groups.
"All of the major actions that the president has taken to reduce gun violence have been challenged," the official said. "And in court after court, the actions are frequently being upheld.
"We have confidence that this is legal."
