The Food and Drug Administration (FDA) sent a warning letter dated February 7 to major drug distributor McKesson for allegedly shipping “illegitimate” opioids to pharmacies and hospitals across the country, CNBC reports.

The news comes as several drug distributors have come under fire for their role in the opioid crisis. In fact, McKesson and its close competitor Cardinal Health are already the subject of numerous lawsuits alleging they flooded communities with opioids, resulting in a major escalation in overdoses, addiction and hepatitis C virus (HCV) infections.

The FDA’s warning letter accuses McKesson of failing to identify, quarantine and investigate drug shipments that had been tampered with, including some that were discovered at three Rite Aid pharmacies in Michigan. In the letter, health authorities cited three instances in which McKesson shipped prescription drugs that were supposed to be opioids but were later discovered to have been removed and replaced with other products.

“A distributor’s failure to have systems in place to investigate and quarantine suspect and illegitimate products within their control is a violation of the law,” said FDA Commissioner Scott Gottlieb, MD, in a recent statement. “This is even more concerning given that we’re in the midst of a widespread opioid crisis.” 

In a statement, McKesson said it takes this situation “very seriously” and has been in contact with the FDA over the past few months about better securing its products and supply chain.

Warning letters are often the first step in regulatory action against a company. This is the first time the FDA has issued a warning letter under the 2013 Drug Supply Chain Security Act, which was established as the opioid crisis was intensifying to prevent situations like this one.