The Wyoming Highway Patrol says its troopers will be on the watch for anyone bringing marijuana from Colorado across the state line.
The patrol put out the warning Tuesday, a day after recreational sales of pot became legal in Colorado.
Spokesman Sgt. Stephen Townsend says no extra patrols are planned but troopers will remain alert as usual for any criminal activity.
People with 3 ounces of pot or less risk being charged with a misdemeanor that carries a penalty of up to 12 months in jail and a fine up to $1,000.