WASHINGTON — According to a letter sent to New York lawmakers late Wednesday, the U.S. Treasury Department has agreed to stop siphoning cash away from the Fire Department’s 9/11 treatment program, but it remains unclear when or if the FDNY would get its missing money back.

The federal agency began docking payments meant to care for ill firefighters and EMTs back in 2016 in a move that was never explained to the FDNY’s World Trade Center Treatment program.

In all, FDNY Chief Medical Officer Dr. David Prezant estimates that $3.7 million that was sent to his program by the National Institute of Occupational Safety and Health simply vanished in transit.

After years of investigation, he learned the Treasury Department was taking the money, apparently to satisfy a wholly unrelated debt dispute between the city and the Centers for Medicare and Medicaid Services, or CMS.

The Treasury Department initially said it was bound by law to take the money, but now says there is a fix.

“Since the issue was brought to our attention, Treasury worked with CMS to suspend offsets for CMS debts pending resolution of this matter,” says the letter addressed to Rep. Carolyn Maloney, D-N.Y. “Treasury is actively engaged with CMS to explore any additional accommodations that can be made to assist FDNY. Ultimately, however, a determination about these accommodations is up to CMS.”

A spokesperson for CMS was unable to say immediately what the agency would do.

The fix identified by The New York Daily News and lawmakers last month is a provision in the law that Treasury cited that says Treasury Secretary Steve Mnuchin can exempt payments if the paying agency involved asks for it.

That would be NIOSH, which, like CMS, is under the Department of Health and Human Services.

Treasury’s letter said it has