MINNEAPOLIS — Medical marijuana supporters face a tough challenge this legislative session in Minnesota, where Gov. Mark Dayton said he won’t sign anything without the backing of law enforcement — and authorities said they’re strongly opposed.

Proponents said medical decisions should be left to doctors, not law officers. Tom Lehman, a lobbyist for marijuana use for the chronically ill, said Minnesota’s proposal would have tight restrictions. He said advocates will try to sit down and with law enforcement.

But Dennis Flaherty, executive director of the Minnesota Police and Peace Officers Association, said authorities don’t support legalizing marijuana for any purpose. He said legalizing medical marijuana would conflict with federal law.

Law enforcement leaders offered no suggestions when asked if there is any provision they might approve.