The White House is to close a loophole that allows thousands of firearms to be sold at gun shows and on the internet without federal background checks.
It will classify around 23,000 vendors as licensed firearms dealers, making their gun sales subject to the checks.
Attorney General Merrick Garland said: “If one sells guns predominantly to earn a profit, one must be licensed.”
The Biden administration said it expected a court challenge by pro-gun groups, but was confident it would win.