The Honolulu Police Department has told legal marijuana users who own guns that they must turn in their weapons within 30 days.

In a letter to about 30 medical marijuana card holders on Oahu, the police said “you have 30 days upon receipt of this letter to voluntarily surrender your firearms.”

Police have been sending the letters since at least January.

One letter was signed by Susan Ballard, the new chief of police, and dated Nov. 13.

“Your medical marijuana use disqualifies you from ownership of firearms and ammunition,” the letter said.

In the letter, Ballard cites Hawaii Revised Statutes, Section 134-7 (a) as the reason for the move. That section reads: “No person who is a fugitive from justice or is a person prohibited from possessing firearms or ammunition under federal law shall own, possess, or control any firearm or ammunition therefor.”