Washington DC - The US Supreme Court appeared likely on Monday to strike down a federal law prohibiting habitual abusers of illegal drugs from owning firearms.

The conservative-dominated court is deciding whether the law violates the Constitution's Second Amendment, which says Americans have the right to keep and bear arms.

The statute – notably used to convict former president Joe Biden's son Hunter – prohibits the possession of firearms by a person who "is an unlawful user of or addicted to any controlled substance" and is punishable by up to 15 years in prison.

Hunter Biden was pardoned by his father shortly before he left office last year.

The Supreme Court, which has a 6-3 conservative majority, tends to rule in favor of gun owners, and after two hours of oral arguments on Monday, a majority appeared inclined to strike down the law.

The case before the court involves Ali Danial Hemani, an alleged habitual marijuana user indicted for being unlawfully in possession of a Glock pistol.

An appeals court ruled that barring Hemani, a dual US-Pakistani national, from owning a gun violated his Second Amendment rights.

Republican President Donald Trump's Justice Department, which generally backs expansive gun rights, challenged that decision.

"The Second Amendment does not prohibit the government from temporarily disarming habitual marijuana users while they persist in using frequently," Principal Deputy Solicitor General Sarah Harris told the court.

This fits in with the "historical tradition" of treating "habitual drunkards" as a class that threatens public safety, Harris said.

Justice Neil Gorsuch, a conservative, pushed back, saying that even early American presidents might have qualified as "habitual drunkards" by the standards of today.

"John Adams took a tankard of hard cider with his breakfast every day," Gorsuch said. "James Madison reportedly drank a pint of whiskey every day... Are they habitual drunkards who would be properly disarmed for life?"

The court is expected to issue its ruling in the Hemani case by late June or early July.