A top Democratic senator is launching an investigation into privately owned methadone clinics’ business practices and treatment of patients.

In letters to three separate for-profit methadone clinic chains, Sen. Maggie Hassan (D-N.H.) is demanding information about revenue, patient volumes, and employee numbers from three major methadone clinic chains: BayMark , New Season , and Acadia .

The investigation, Hassan wrote, seeks to “better understand the impact of the OTP model on patient access to methadone; patient treatment outcomes; and potential waste, fraud, and abuse in federal health care programs.”

The effort comes amid increasing scrutiny of methadone clinics in Washington and across the nation. Amid the opioid overdose crisis, the methadone clinics have come under fire for

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