Filed in the U.S. District Court for the Northern District of Illinois, the complaint says the drugstore chain’s pharmacists filled controlled substance prescriptions with clear red flags that indicated they were highly likely to be unlawful. Walgreens also systematically pressured pharmacists to fill prescriptions without taking the time to confirm their validity, according to the complaint.

The lawsuit says Walgreens filled “unlawful” prescriptions in violation of the federal Controlled Substances Act and sought reimbursement from federal health care programs for them in violation of the False Claims Act.

Walgreens, one of the country’s largest pharmacy chains, with over 8,000 locations, said in a statement that it stands behind its pharmacists. It said they say fill legitimate prescriptions for Food and Drug Administration-approved medications written by Drug Enforcement Administration-licensed prescribers in accordance with all applicable laws and regulations.

Walgreens is also accused of ignoring evidence, including from its own pharmacists and internal data, that stores were dispensing unlawful prescriptions, according to the complaint. In addition, it allegedly deprived pharmacists of crucial information including by preventing them from warning each another about particular prescribers.

“This lawsuit seeks to hold Walgreens accountable for the many years that it failed to meet its obligations when dispensing dangerous opioids and other drugs,” Principal Deputy Assistant Attorney General Brian M. Boynton, head of the Justice Department’s Civil Division, said in a statement. “These practices allowed millions of opioid pills and other controlled substances to flow illegally out of Walgreens stores.”

The company said it is asking the court to clarify the responsibilities of pharmacies and pharmacists and to protect against the government’s attempt to enforce arbitrary “rules” that do not appear in any law or regulation and never went through any official rulemaking process.

“We will not stand by and allow the government to put our pharmacists in a no-win situation, trying to comply with “rules” that simply do not exist,” Walgreens said in the statement.

The company also said it has been a leader in providing education and resource, as well as implementing the best policies and procedures to help combat opioid misuse.

The DOJ filed a similar lawsuit against CVS in December. A spokesperson for that chain has said it strongly disagrees with the allegations and what it called a “false narrative” in the complaint.

Federal prosecutors have been trying to hold companies accountable for their alleged roles in the U.S. addiction and overdose crisis, with opioids tied to over 80,000 annual deaths in some recent years.

During the past decade, most of those deaths have mostly been attributed to illicit fentanyl, which is laced into many illegal drugs. Prescription pills were the primary cause earlier.

Over the past eight years, drugmakers, wholesalers and pharmacies have agreed to approximately $50 billion in settlements with governments, with the majority of the money going toward fighting the crisis.