Federal prosecutors have told the city of Oakland, California, that they will prosecute pot farmers operating under the city's planned marijuana licensing scheme.

A letter from US Attorney Melinda Haag said the city's ordinance, which city council passed last year, breaks federal law and opens marijuana growers to prosecution.

And in a reference that some have interpreted as a threat to Oakland's officials and city councilors, Haag also warned that anyone who "knowingly facilitates" marijuana cultivation could also be prosecuted.

"It was unclear whether Haag meant to warn or threaten Oakland's individual City Council members, or other city employees or property," the Oakland Tribune reported. "A spokesman for Haag declined to comment Wednesday beyond what was said in the letter."

The Bay Area city gained national attention last year when councilors proposed and passed an ordinance that allowed for four marijuana farms in the city limits, each unlimited in size. Supporters argued Oakland, which last year faced a $42 million budget shortfall, could earn as much as $1 million annually from tax revenue generated by the farms.

But after city lawyers suggested the plan could violate federal law, the ordinance was shelved. It was this ordinance that Haag commented on in her letter, but city councilors say a new version of the law, which caps the size of each farm at 50,000 square feet, may escape prosecution.

That's because, as Haag noted in her letter, federal authorities don't pursue ill people who consume marijuana when allowed under state law. Under California law, marijuana can be cultivated by sick people with prescriptions or their "primary caregivers."

Under the new ordinance, the marijuana farms would be tied to a particular pot dispensary and the dispensary would be labeled as the marijuana consumers' "primary caregivers," thus allowing them to operate as suppliers, reports the San Francisco Chronicle.

While state voters authorized the use of medical marijuana in 1996, little has been done to regulate its cultivation. The result is a hodgepodge of basement plots, vacant storefront mini-farms and backwoods plantations. Critics, including the City Council, say keeping the industry in the black market invites ad hoc electrical systems, burglaries and home invasions.

Oakland's plans include inspections of growing sites for fire and safety codes, among a slew of other requirements.

"The whole point of the regulatory system is to keep this out of the hands of criminal cartels and protect public safety," Councilwoman Rebecca Kaplan, author of the original ordinance, told the Chronicle.