Citibank sent a hedge fund of $175 million by mistake, and they can't get it back.

Citibank mistakenly wired roughly $175 million to Brigade capital management, a global alternative investment manager specializing in credit investment strategies, and the hedge fund hasn't returned the money.

The US banking Giant filed a lawsuit on Monday in the Southern District of New York, seeking the return of funds that it said were transferred in an "operational mistake."

Citibank said in court documents that it meant to send Brigade Capital around $1.5 million in interest payments on a loan the hedge fund made to troubled cosmetics company Revlon (REV). instead, it wired roughly 100 times that amount of its own funds to the hedge fund. Other Revlon creditors also received erroneous payments, adding up to $900 million.

Citibank, which acts as an administrative agent on the Revlon loan, alleges in court documents that Brigade Capital is refusing to return the money. "Brigade has taken the baseless position that Citibank's overpayments... served to pay off Revlon's entire principal balance as well,"

To support that allegation, the bank includes a message purportedly sent by Brigade Capital that says it's "not at all clear that the funds were sent as a result of 'clerical mistake.' "

Citigroup has won a temporary court order freezing that $175 million that Brigade Capital Management LP is refusing to return.