United States Attorney Laura Duffy
United States Attorney Laura Duffy displays a photo of marijuana cotton candy while announcing law enforcement action against California's marijuana industry in Sacramento October 7, 2011. Reuters

Federal prosecutors announced a crackdown on Friday on what they called California's massive commercial marijuana industry, including medical pot dispensaries they say are often fronts for illegal for-profit drug distribution.

Measures will include civil forfeiture lawsuits against properties involved in drug trafficking, warning letters sent to landlords of storefronts illegally selling marijuana, and criminal cases targeting cannabis activities across the state.

The move was announced by four U.S. attorneys and marks an escalation in the friction between the federal government and California, which in 1996 became the first state to legalize marijuana for medical purposes.

Fifteen other states and the District of Columbia have since enacted similar statutes.

The prosecutors said California's medical marijuana law has given cover for large-scale commercial operations to engage in drug trafficking across state lines, with thousands of pounds of marijuana worth tens of millions of dollars flowing across the country from California.

That is not what the California voters intended or authorized, and it is illegal under California law, said Andre Birotte, U.S. attorney for the Central District of California.

Supporters of medical marijuana said the federal enforcement actions were unfairly targeting patients and suppliers operating legally under state law.

The Obama administration's latest moves strongly suggest that their medical marijuana policies are now being driven by over-zealous prosecutors and the anti-marijuana ideologues who dominated policymaking in past administrations, Ethan Nadelmann, executive director of the Drug Policy Alliance, said in a statement.

Instead of encouraging state and local authorities to regulate medical marijuana distribution in the interests of public safety and health, his administration seems determined to re-criminalize as much as possible. he said. It all adds up to bad policy, bad politics and bad faith.

Reversing the position taken by the Justice Department under President George W. Bush, the Obama administration said in October 2009 that federal attorneys would no longer prosecute patients who use pot, or dispensaries that distribute it, for medical reasons in states where it has been legalized.

But that memo was never intended to shield commercial operations or industrial-size growth, said Melinda Haag, U.S. attorney for the Northern District of California.

People are using medical marijuana to make tons of money, and sometimes engage in drug trafficking, Haag said.

Cannabis is considered an illegal narcotic under U.S. law, and federal authorities, have raided pot dispensaries and greenhouses in California, Montana and other states in a crackdown aimed at supposed medical marijuana suppliers engaged in large-scale drug trafficking.