Stiff fines have been issued, and at least one company has declared bankruptcy as the US continues to pursue its case against opioid manufacturers, blaming them for the “epidemic” that has reportedly claimed 400,000 lives across the country since 1999.

Now the newspaper Wall Street Journal, (WSJ), quoting sources, reports that federal prosecutors, employing laws normally used to go after drug dealers, have opened a criminal investigation into whether pharmaceutical companies intentionally allowed opioid painkillers to flood communities.

If the investigation does result in criminal charges, it could become the largest prosecution ever of drug companies alleged to have contributed to the opioid epidemic, WSJ notes, thus escalating the legal troubles of businesses that already face complex, multibillion-dollar civil litigation in US courts.

Prosecutors are said to be examining whether the companies violated the US Controlled Substances Act. In this connection, at least six companies, including drugmakers Teva Pharmaceuticals, Mallinckrodt, Johnson & Johnson and Amneal Pharmaceuticals, along with distributors AmerisourceBergen Corp and McKesson have said in regulatory filings that they have received subpoenas from the U.S. attorney’s office in the Eastern District of New York.

According to previous press reports, the targeted companies have denied responsibility for the opioid crisis. WSJ’s sources said additional companies will receive subpoenas in the coming months.

Under the Controlled Substances Act, companies are required to monitor commonly abused drugs, including by reporting suspicious orders, maintaining compliance programs and disclosing suspicious pharmacy customers to the government.

Almost every US state and more than 2,500 city and county governments have filed lawsuits against players across the opioid supply chain. The state of Ohio has settled with four companies, and hundreds of other lawsuits bundled in a Cleveland, Ohio, federal court are still pending settlement.