Senate Democrats urged the nonpartisan Congressional Budget Office to check the Trump administration’s math when it comes to Iran war costs — accusing officials of lowballing.

The group of 20 lawmakers, led by Sens. Elizabeth Warren of Massachusetts, Chuck Schumer of New York and Jeff Merkley of Oregon, is pressing the budget watchdog to scrutinize what they argue is the big gap between the administration’s public estimates for the war and outside analyses that put the price tag tens of billions of dollars higher.

“We are concerned that the administration has not been fully truthful or transparent in its public accounting of the war’s costs so far,” the senators wrote in a letter sent Wednesday to CBO Director Phillip Swagel.

The sharp appeal from Senate Democrats lands as the political and economic fallout from the nearly 3-month-old conflict continues to mount. Acting Pentagon Comptroller Jay Hurst told lawmakers this month the war’s cost had jumped from $25 billion weeks earlier to $29 billion, despite a ceasefire technically in place.

Democrats seized on reports that the Pentagon’s figure excludes billions more in damage to U.S. military installations and destroyed equipment across the Middle East. The lawmakers pointed to outside estimates ranging from $35 billion to roughly $72 billion, once higher energy prices and the long-term care for veterans are factored in.

The dispute over the war’s cost is part of a broader fight over the administration’s handling of the conflict ahead of November’s midterm elections. Beyond the administration’s $1.5 trillion defense budget request, it’s considered requests for supplemental funding in the $200 billion and $100 billion ranges.

The letter comes amid reports Thursday that U.S. and Iranian negotiators reached a tentative agreement to extend the ceasefire by another 60 days to further negotiate Iran’s nuclear program. The ceasefire appeared fragile as the U.S. military accused Tehran of firing missiles toward Kuwait after U.S. strikes on Iranian drone and missile sites near the Strait of Hormuz.

The Congressional Budget Office hasn’t publicly acknowledged whether it would probe the Iran conflict’s cost, but it generally responds to requests from lead lawmakers. CBO officials have acknowledged difficulties in recent months obtaining information from the Pentagon, but Schumer’s involvement, because he is the Senate minority leader, suggests it is likely to be a top priority for the agency.