Federal authorities in California are cracking down on the state's medical marijuana industry, four U.S. attorneys in the state announced.

Prosecutors have stepped up campaigns to break up businesses that take shelter under a state law allowing patients to possess marijuana for medical use, sending warning letters, filing civil forfeiture lawsuits, and prosecuting criminal cases, the attorneys said.

"It's the new California gold rush," Andre Birotte Jr., the U.S. attorney for the state's central district, said during a press briefing. "There's an epidemic of these marijuana stores."

Authorities said a large for-profit marijuana industry has developed since the state passed Proposition 215 in 1996, which enabled patients with medical needs for marijuana -- dictated by illnesses such as cancer or AIDS -- to possess the drug for therapeutic relief.

They emphasized, however, that they will focus their efforts on curbing illegal activity, and patients in need of the drug will still be able to get it.

The campaign kicked off with a round of warning letters sent to property owners where marijuana is being grown or sold, giving them 45 days to halt their operations, according to reports.

Prosecutors have also seized bank accounts maintained by some of the marijuana stores, and have filed civil forfeiture complaints against properties, including two in Bakersfield and Fresno.

The Bakersfield operation, American Green Farmers Collective, allegedly turned a profit of $100,000 per month, according to Benjamin Wagner, U.S. attorney for the eastern district.

Several criminal cases have also been initiated, including one against a Los Angeles attorney who allegedly used his law office as a front to conduct a pot-selling business. Another case has been filed against a Florida man who moved to California to allegedly start a marijuana cultivation business. Finally, a case has been initiated against a father-and-son team who were alleged to have made a profit of $30,000 to $50,000 per day from marijuana sales.

Birotte said there are more than 1,000 marijuana stores in the central district of California alone.

"Large commercial operations cloak their moneymaking activities in the guise of helping sick people when in fact they are helping themselves," Wagner said. "Our interest is in enforcing federal criminal law, not prosecuting seriously sick people and those who are caring for them."

Laura Duffy, the U.S. attorney for the state's southern district, said California's marijuana industry "is not about providing medicine to the sick. It's a pervasive for-profit industry that violates federal law."

The Drug Enforcement Agency (DEA) and the Internal Revenue Service also announced their support of the initiatives, with the DEA emphasizing in a statement that it has little tolerance for drug trafficking operations "that attempt to use state or local law to shield their illicit activities from federal law enforcement and prosecution."