The U.S. Justice Department sued Walmart Inc on Tuesday, accusing the retailer of fueling the opioid crisis in the United States and ignoring warning signs from its pharmacists, according to a court filing.

The retailer’s shares fell about 2% following the news.

The lawsuit, filed in U.S. District Court in Delaware, accused Walmart of failing to take its gatekeeping duties as a pharmacy seriously.

Walmart, the world’s biggest retailer, created a system that turned its 5,000 in-store pharmacies into a supplier of highly addictive painkillers, dating as early as June 2013, the lawsuit said.

Walmart’s actions helped “fuel a national crisis,” said Jeffrey Bossert Clark, the acting head of the Justice Department’s civil division, who declined to say how much precisely the government was seeking in penalties from Walmart.

Walmart declined to immediately comment on the lawsuit.

The government’s complaint said “Walmart managers put enormous pressure on pharmacists to fill prescriptions – requiring pharmacists to process a high volume of prescriptions as fast as possible, while at the same time denying them the authority to categorically refuse to fill prescriptions issued by prescribers the pharmacists knew were continually issuing invalid prescriptions.”

In October, the retailer filed a lawsuit against the federal government seeking clarity on the roles and legal responsibilities of pharmacists and pharmacies in filling opioid prescriptions.

The opioid epidemic has claimed the lives of roughly 450,000 people across the United States since 1999 due to overdoses from prescription painkillers and illegal drugs. (Reporting by David Shepardson and Mark Hosenball in Washington, Nivedita Balu in Bengaluru