Chemical bank Optum Bank says it’s a “black box” threat, saying the company “should have been aware” of its role in a scandal that could have jeopardized billions of dollars in deposits.

In a memo sent to investors, Optum’s chief executive officer, John Steed, said the bank has “serious concerns” about how Optum handled a $1.9 billion loan from the company that could potentially have resulted in the company losing its security rating.

Steed told investors the bank was “very concerned” about a potential regulatory impact if Optum failed to get the loan back from the bank.

Optum also said it has asked the Department of Justice to investigate the matter and has asked Optum to disclose more information.

“The Optum board is a diverse group of investors, including members of the American Bankers Association, National Association of Banking Supervisors, and Credit Suisse Group AG, among others, and we will continue to cooperate with the appropriate authorities to ensure that our investors are protected from any potential legal liability,” Steed said in the memo.

Optum has not yet responded to a request for comment.