WASHINGTON — Thousands more firearms dealers across the United States will have to run background checks on buyers at gun shows or other places outside brick-and-mortar stores, according to a Biden administration rule that will soon go into effect.

The rule aims to close a loophole that has allowed tens of thousands of guns to be sold every year by unlicensed dealers who do not perform background checks to ensure the potential buyer is not legally prohibited from having a firearm. Gun rights groups are expected to fight it in court.

It’s the administration’s latest effort to combat gun violence. But in a contentious election year, it’s also an effort to show voters — especially younger ones for whom gun violence deeply resonates — that the White House is trying to stop the deaths.

“This is going to keep guns out of the hands of domestic abusers and felons,” President Joe Biden said in a statement. “And my administration is going to continue to do everything we possibly can to save lives. Congress needs to finish the job and pass universal background checks legislation now.”

The rule, which was finalized this week, makes clear that anyone who sells firearms predominantly to earn a profit must be federally licensed and conduct background checks, regardless of whether they are selling on the internet, at a gun show or at a brick-and-mortar store, Attorney General Merrick Garland told reporters.

Biden has made curtailing gun violence a major part of his administration and reelection campaign, creating the White House Office of Gun Violence Prevention overseen by Vice President Kamala Harris. Biden also has urged Congress to ban so-called assault weapons — something Democrats shied from even just a few years ago.

The rule is likely to be challenged in court by gun rights activists who believe the Democratic president is unfairly targeting gun owners. The National Rifle Association said in a statement that it is “already working to use all means available to stop this unlawful rule.”

The National Shooting Sports Foundation, an industry trade group, also has warned of a court challenge if the rule was finalized as written. Lawrence Keane, the foundation’s senior vice president and general counsel, said Thursday that the organization was reviewing the regulation after contending previously that the Bureau of Alcohol, Tobacco, Firearms and Explosives was overstepping its legal authority.

Biden administration officials said they are confident the rule, which drew more than 380,000 public comments, would withstand lawsuits.

The administration first proposed the rule in August, after the passage of the most sweeping gun violence bill in decades, a bipartisan compromise in response to the massacre of 19 students and two teachers at a Uvalde, Texas elementary school.

That law expanded the definition of those who are “engaged in the business” of selling firearms, and are required to become licensed by the ATF and therefore run background checks. The rule, which implements the change in the law, will take effect 30 days after it is published in the Federal Register.

There are already roughly 80,000 federally licensed firearms dealers. Administration officials believe the new rule will impact more than 20,000 dealers who have gotten away with selling firearms without a license and performing background checks at places like gun shows and over the internet by claiming they aren’t “engaged in the business” of firearm sales.

“Everybody can see that people are not following the law in significant numbers,” ATF Director Steve Dettelbach said in an interview. “And it’s just wrong for public safety, it’s wrong for fairness when all these licensed dealers are out there following the rules, for people to think that they don’t have to all play by the same set of rules.”