Firearms dealers in states that allow medical marijuana can't sell guns or ammunition to registered users of the drug, a policy that marijuana and gun-rights groups say denies Second Amendment rights to individuals who are following state law.
Federal law already makes it illegal for someone to possess a gun if he or she is "an unlawful user of, or addicted to" marijuana or other controlled substances.
A Sept. 21 letter from the Bureau of Alcohol, Tobacco, Firearms and Explosives, issued in response to numerous inquiries from gun dealers, clarifies that medical marijuana patients are included in that definition.
"There are no exceptions in federal law for marijuana purportedly used for medicinal purposes, even if such use is sanctioned by state law," said the letter by Arthur Herbert, the ATF's assistant director for enforcement programs and services.
Federal firearm licensees, or FFLs, can't sell a gun to someone who answers "yes" when a required form asks whether the buyer is a controlled substance user.
'Reasonable cause to believe'
Last week's letter also says that licensed dealers can't sell a gun or ammunition if they have "reasonable cause to believe" the buyer is using a controlled substance.
That includes if the buyer presents a medical marijuana card as identification, or if the buyer talks about drug use, having a medical marijuana card or a recent drug conviction, ATF spokesman Drew Wade said Wednesday.
But there are no new obligations for gun dealers outlined in the letter, Wade said.
"We received lots of queries from the industry from various states of how to deal with state legislation and the federal law," he said. "It's our responsibility to provide advice and guidance."
The clash between state and federal drug laws has led to lawsuits and criminal cases in some of the 16 states that have legalized medical marijuana use.
Officials in two Oregon counties have said they'll appeal to the U.S. Supreme Court after state judges said sheriffs couldn't deny concealed handgun licenses for medical marijuana patients.
The Oregon Court of Appeals and the Oregon Supreme Court said the state law that authorizes concealed handgun permits is separate from the federal law that outlaws gun possession by drug users, and the state gun law doesn't address medical marijuana use.
Federal authorities also raided dozens of medical marijuana operations across Montana this spring, chilling a once-booming pot industry and leading to sweeping changes in Montana law.
The Department of Justice followed up with a warning letter to political leaders in many states that federal prosecutors will pursue marijuana distributors but not individual patients who are following state law.
The letter the ATF sent to gun dealers last week was first reported by Lee Newspapers of Montana.
Pro-marijuana and gun groups said the policy clarification amounts to rescinding the gun rights for the thousands of people licensed to use medical marijuana laws.
And it appears to contradict a 2009 Department of Justice memo that said the Obama administration would not pursue prosecution of individual medical marijuana users who obey state laws.
Besides that, the government is putting an additional burden on gun dealers to police their customers, said Montana Shooting Sports Association Gary Marbut.
"Their business is to be merchants, not to be cops. Unfortunately, the federal licensing scheme complicates that," Marbut said. "It sounds as if the (ATF) is expecting them to drift further into the cop role."
'Protecting America from criminals'
Wade said both the 2009 memo and last week's letter were approved by the Justice Department and he does not believe there is a contradiction in the two messages.
He also that the dealers are in a good position to help prevent firearms from getting into the wrong hands.
"The FFLs aren't cops but they are at the front line of protecting America from criminals or people who are prohibited from possessing firearms," Wade said.
A salesman at one licensed firearms dealer, Montana Outdoor Sports in Helena, said he doesn't expect much to change as a result of the letter because it's largely up to the buyer to reveal whether he or she is a medical marijuana user.
"Who's going to say yes to that?" asked Damon Peters, a sales associate for the store and a licensed hunting guide.
"A lot of users of medical marijuana aren't really shooting sports enthusiasts, anyway. I think we may see a sale or two lost, but I don't see anything dramatic that's going to affect us," he said.