Federal law states it is illegal to possess a firearm if you use a controlled substance. Marijuana -- even medical marijuana -- is considered a controlled substance.

In a response to multiple gun dealers, the Bureau of Alcohol, Tobacco, Firearms and Explosives explained, "There are no exceptions in federal law for marijuana purportedly used for medicinal purposes, even if such use is sanctioned by state law."

Sixteen states, including California have legalized medical marijuana. The state has issued almost 57,000 medical marijuana cards, according to the California Department of Public Health.

Gun rights advocates and medical marijuana advocates are saying this policy is a violation of the second amendment right to keep and bear arms.

Licensed gun dealers cannot sell a gun or ammunition to anyone that indicates on the paperwork that they are using a controlled substance, or if the dealer has a "reasonable cause to believe" person uses drugs. Reasonable cause includes even talking about drugs.

In an interview with the Associated Press, Gary Marbut with the Montana Shooting Sports Association said this puts an unreasonable burden on gun dealers to police their customers.

"Their business is to be merchants, not to be cops. Unfortunately, the federal licensing scheme complicates that. It sounds as if the (ATF) is expecting them to drift further into the cop role," Marbut said.

The Justice Department however believes that part of the responsibility of selling guns is to keep them away from people who are prohibited from having them.

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