The ordinance, passed unanimously by City Council late on Monday, bans all outdoor advertising by the city's 400 medical pot shops, but allows ads in print publications and online sites, although they must contain a disclaimer noting that cannabis products are for medical use only.

  Colorado's November ballot measure would legalize up to an ounce (28 grams) of marijuana for recreational use, despite a federal ban on the drug. Oregon and Washington state are voting on similar measures. 

Federal law enforcement under the Obama administration has cracked down on dispensaries in several Western states that allow medical pot operations.

  Deborah Ortega, an at-large councilwoman who sponsored the law, said she had explored crafting an ordinance banning outdoor advertising within 1,000 feet of schools, parks and daycare centers, but decided on the outright ban. 

"The intent was to protect kids," Ortega told Reuters on Tuesday.