Investigators from the FBI and the Department of Defense are reportedly looking into allegations that Universal Health Services — the nation’s largest provider of inpatient psychiatric care, with nearly 200 facilities in 38 states and Puerto Rico — is padding its bottom line by deliberately holding patients longer than is medically necessary.

This is according to BuzzFeed News, citing sources with direct knowledge of an investigation into concerns about whether or not UHS used these alleged practices to overbill government plans like Medicare, Medicaid, and Tricare, the healthcare plan administered by the Defense Health Agency.

More than a dozen individual UHS facilities and the company’s corporate operation are being investigated, per BuzzFeed, for potential violations of the False Claims Act, which prohibits individuals and companies from knowingly submitting bogus requests for payment to the federal government.

Like many healthcare facilities, UHS hospitals bill insurance providers based on the number of days a patient remains under the facility’s care. So the longer the stay, the larger the bill.

BuzzFeed first raised concerns about overlong stays at UHS hospitals last December in a report claiming that current and former employees from multiple UHS facilities said they had been told to not “leave days on the table” — in other words, to maximize revenue by not releasing patients until the insurance company stopped paying.

At the company’s recent annual meeting, some nurses protesting conditions at UHS facilities claimed that there have been times when they told a doctor that a patient was ready for release, only to be asked how much longer their insurance would cover their stay. That “last covered day” would ultimately be the day of release, alleged the nurses, who said that doctors would have to occasionally revise a patient’s notes to justify the longer stay.

“If they’re on Medicare or Medicaid, they’ll milk it,” said one nurse.

Added a second, “They’ll admit people just to fill a bed.”

In a statement to BuzzFeed, UHS has said it “absolutely rejects” the allegations in these reports.

In 2012, UHS agreed to pay $6.85 million to settle a Justice Department False Claims Act lawsuit that originated as a whistleblower complaint filed by multiple UHS employees.

The DOJ alleged [PDF] in 2010 that Universal had overbilled government insurance programs by, among other things: billing for services for which there was no documented evidence; billing for group therapy sessions that didn’t occur; having unqualified staff hold therapy sessions that were then billed as if a qualified therapist had conducted the sessions. Most relevant to the allegations in the BuzzFeed reports were the claims that UHS staff would “provoke” patients with the intention of getting a reaction that would justify a longer stay (and thus more money from Medicaid).

Though UHS settled these claims with the government, it did not admit to any wrongdoing.

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