The California Department of Health Care Services announced an investigation of 16 substance abuse treatment centers for patients on Medi-Cal, the state’s insurance plan for people on welfare and other low-income residents. The centers are suspected of fraud and hiring providers who have felonies on their records.

According to the department, the clinics billed Medi-Cal for services that were not medically necessary, and charged for services they did not offer, the Los Angeles Times reports. The department is also investigating whether workers hired some employees who had been convicted of neglecting and abusing patients at other health centers, the article notes.

The centers will remain open, but will not be receiving funds from Medi-Cal during the investigation. Norman Williams, who heads the communications office at the department, said one of the investigation’s goals is “to minimize patient harm because it’s not just about the money, but the people, to make sure they’re getting adequate care. We want to make sure that people know that we’re monitoring this closely and ensuring the safety of our members.”

The California Department of Justice is investigating the centers. Sanctions could range from temporarily suspending providers from submitting claims for reimbursement of services, to permanently suspending them from participation in Medi-Cal, according to a news release.