MANTECA — Medicinal marijuana dispensaries have effectively been banned within the City of Manteca, after the City Council crafted a new rule that exploits a conflict between state and federal law.

The new ordinance, which simply states that the city will not issue a license for any business that violates local, state or federal law, was ratified May 5 by a unanimous council vote.

Though councilmen did not discuss the law before voting — and an accompanying staff report offered little explanation — Interim Police Chief Dave Bricker said its main purpose was to pre-empt medicinal marijuana dispensaries.

Marijuana dispensaries, also known as cannabis clubs, are legal under state but not federal law.

The clubs have sprung up across the state since 1996, when voter-approved Proposition 215 changed state law to allow patients to grow or buy marijuana with a doctor’s approval.

Since then, pot clubs have caused headaches for many cities, and local governments have used a variety of means to pre-empt the clubs or force them out.

The City of Tracy closed down a dispensary last year on grounds that it was not listed as one of the city’s accepted retail activities.

Mayor Willie Weatherford said the police department suggested the new law to prevent dispensaries from opening in town.

“They felt the law (in Manteca) needed to be tightened up,” Weatherford said.

Bricker said the new law could also be used to combat prostitution rings, which often operate with a business license as a massage parlor or escort service.

In these cases, Bricker said, the city would only revoke a business license after a full police investigation produced “overwhelming evidence” that a crime was taking place.

A San Francisco escort service has recently applied to open up shop in Manteca, Bricker said, and several people inquired about opening a cannabis club in town several months ago.