WASHINGTON — The Justice Department sued Walmart on Tuesday, accusing it of fueling the nation's opioid crisis by pressuring its pharmacies to fill even potentially suspicious prescriptions for the powerful painkillers.

The civil complaint filed points to the role Walmart's pharmacies may have played in the crisis by filling opioid prescriptions and Walmart's own responsibility for the allegedly illegal distribution of controlled substances to the pharmacies at the height of the opioid crisis.

The Justice Department alleges Walmart violated federal law by selling thousands of prescriptions for controlled substances that its pharmacists “knew were invalid,” said Jeffrey Clark, the acting assistant attorney general in charge of the Justice Department's civil division.

Federal law required Walmart to spot suspicious orders for controlled substances and report those to the Drug Enforcement Administration, but prosecutors charge the company didn't do that.

“Walmart knew that its distribution centers were using an inadequate system for detecting and reporting suspicious orders,” said Jason Dunn, the U.S. attorney in Colorado. “As a result of this inadequate system, for years Walmart reported virtually no suspicious orders at all. In other words, Walmart's pharmacies ordered opioids in a way that went essentially unmonitored and unregulated.”

The 160-page suit alleges that Walmart made it difficult for its pharmacists to follow the rules, putting “enormous pressure” on them to fill 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.