In late June, a gun store in Charlemont, Massachusetts, posted a letter on Facebook from the Bureau of Alcohol, Tobacco, Firearms and Explosives.

The 2011 letter notified gun dealers that just because someone has a state medical marijuana card, it doesn't mean it's legal for them to purchase a gun.

Charles Ricko, who owns Overwatch Outpost Outfitters, said he decided to post the letter after hearing confusion among some gun owners.

"We've had several people come into the store," he said. "They haven't purchased guns, but people have made statements such as, 'I'm a medical marijuana cardholder,' and that marijuana is legal in Massachusetts now, so it shouldn't affect them with buying a gun."

But it does.

To buy a firearm, a person first has to fill out a form. It asks a series of questions, like whether they've ever been convicted of a felony, been committed to a mental institution, or are an unlawful user of marijuana.

And in the federal government's eyes, any use of marijuana is unlawful.

A question from the revised "Firearms Transaction Record" that must be completed by gun buyers and sellers. As of October 2016, it included new language related to marijuana use. (Form 4473/ATF)

Matthew O'Shaughnessy, who works for the ATF's Boston office, said the bureau decided to make that even clearer.

"Certain states have legalized the use of marijuana, and ATF wanted to let federal firearms licensees know — remind them — that it's still illegal federally to use marijuana," he said.

So in 2016, the ATF decided to add some bold print to that questionnaire, warning that pot remains illegal under federal law — the state law does not matter.

Maggie Kinsella, with the Massachusetts Cannabis Reform Coalition, said the group doesn't have a position on limitation, but she personally sees it as unfair.

"There's no restriction on alcohol consumption and gun rights, so this is just one more thing they're trying to do to blockade cannabis consumers and put them into a lower class of citizenship," she said. "It's not right."

But unless Congress changes the law, the ATF will keep enforcing it. O'Shaughnessy said the marijuana question isn't something to be trifled with.

"If you answer falsely on this question here, on 'question e,' if you answer no and you actually are, you're subject to a felony charge for lying on a federal form," he said.

O'Shaughnessy said no one has been arrested in Massachusetts for answering the question falsely.

New England Public Radio's Carrie Healy contributed to this report.

This story is a production of the New England News Collaborative and was originally published by New England Public Radio.