Federal prosecutors announced Friday a broad and aggressive crackdown of medical marijuana in California on the grounds that some criminals are using pot dispensaries for drug trafficking.

The move angered medical marijuana advocates who said the crackdown was an assault on medical marijuana patients' rights and their ability to access medicine.

President Barack Obama’s to Justice Department Official, Attorney General Eric Holder had previously indicated prosecutors would not target medical marijuana users and caregivers, provided they followed states laws.

"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. It all adds up to bad policy, bad politics and bad faith," said Ethan Nadelmann, executive director of the Drug Policy Alliance in a statement.

At a news conference in Sacramento today, U.S. Attorney Melinda Haag and three other U.S. attorneys said many of the drug trafficking ventures are using California's medical marijuana law to operate in plain sight, according to the Associated Press.

Prosecutors stated that thousands of pounds of marijuana worth tens of millions of dollars flow across the country from California as far as New York.

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

California became the first U.S. state that allowed marijuana consumption for medical purposes in 1996.

Marijuana dispensaries generate sales of as much as $1.3 billion a year and sales taxes of as much as $105 million annually, according to California's Board of Equalization, Bloomberg reports.

The crackdown 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, Prosecutors said.