United States attorneys in California have told dozens of marijuana dispensaries they must close or face criminal and civil action. The move is part of a crackdown on California’s medical marijuana industry, The New York Times reports.

On Friday, four U.S. attorneys said they would prosecute landlords who rent space to operators of medical marijuana dispensaries. The attorneys said they suspect these dispensaries of using the state’s medical marijuana law to profit from large-scale drug sales. They said tens of millions of dollars’ worth of the drug is being sent across state lines.

The attorneys said they are also focusing on properties used to grow marijuana.

California legalized medical marijuana in 1996, the first state to do so, the article notes. There are now 15 other states with similar laws.

Medical marijuana advocates said the move will push the medical marijuana market underground.

The attorneys emphasized they will not focus their efforts on individual patients. “Large commercial operations cloak their money-making activities in the guise of helping sick people when they are in fact helping themselves,” said Benjamin B. Wagner, the U.S. attorney in Sacramento. “Our interest is in enforcing federal criminal law, not prosecuting seriously ill sick people and those who are caring for them.”

In July, the U.S. Justice Department announced that medical marijuana dispensaries and licensed growers located in states with medical marijuana laws are not immune from prosecution for violation of federal drug and money-laundering laws. Deputy Attorney General James Cole wrote a policy memo to federal prosecutors that states, “Persons who are in the business of cultivating, selling or distributing marijuana, and those who knowingly facilitate such activities, are in violation of the Controlled Substances Act, regardless of state law.”