The military admitted last week that it failed to “adequately” charge the Saudi-led coalition in Yemen for “fuel and refueling services” in the war in Yemen, an oversight costing potentially tens of millions of dollars, The Atlantic reported.

That Saudi-led war has depended on American fuel and mid-flight refueling missions; it’s also created the largest humanitarian crisis in the world. Senators are set to vote this week on whether to continue America’s involvement in the war.

“Although DoD has received some reimbursement for inflight refueling assistance provided to the Saudi-led coalition (SLC), U.S. Central Command recently reviewed its records and found errors in accounting where DoD failed to charge the SLC adequately for fuel and refueling services,” a Pentagon spokesperson admitted to The Altantic.

The admission came in response to the magazine obtaining an internal Defense Department letter from Nov. 27, the conclusions of which were made after a request for information from Sen. Jack Reed (D-RI), according to the report.

Per The Atlantic, the letter states that while the Pentagon “believed” both Saudi Arabia and the United Arab Emirates “had been charged for the fuel and refueling services, they in fact had not been charged adequately.”

“It is clear that the Department has not lived up to its obligation to keep Congress appropriately informed or its responsibility to secure timely reimbursement,” Reed said of the news, adding: “U.S.-provided aerial refueling assistance was provided to the Saudi-led coalition for more than 3.5 years, activities that likely cost tens of millions of dollars. We must ensure that U.S. taxpayers are fully reimbursed for that support.”

