The Trump administration has temporarily frozen and ordered a review of several key foreign aid funds that Congress has already approved, in a move that critics fear could lead to another attempted rollback of foreign aid.

The Office of Management and Budget sent a letter to the State Department and the U.S. Agency for International Development on Saturday, notifying them of the action, which took effect one minute before midnight that day.

The OMB asked the agencies for a balance sheet of foreign aid projects that have not yet been funded. Michael P. Duffey, the associate director for national security programs at OMB, wrote that no more money can be obligated from those funds until three days after OMB receives the numbers, a process that could take days if not weeks.

The letter, viewed by The Washington Post, lists eight areas that cover a variety of assistance: international organizations; peacekeeping operations and activities; international narcotics control and law enforcement; development aid; assistance for Europe, Eurasia and Central Asia; economic support funding; foreign military financing programs; and global health programs.

An administration official said the funds targeted for review are above budgetary limits proposed by President Trump. They include big-ticket items like contributions to the United Nations and smaller items like solar panels in the Caribbean, schools in Uzbekistan and soccer programs in Central America.

Traditionally, a significant portion of foreign aid funding is obligated toward the end of a fiscal year, which runs through Sept. 30. But this year the pot is bigger, in part because the administration has cut aid to the Northern Triangle countries of Guatemala, Honduras and El Salvador, and for the Palestinians.

According to people familiar with the process, the named funds could be as little as $2 billion and as much as $4 billion.

The State Department and USAID declined to comment, referring questions to OMB.

“It is incumbent on all federal agencies to properly use funds provided by Congress,” said Rachel Semmel, the OMB spokeswoman. “In an effort to ensure accountability, OMB has requested the current status of several foreign assistance accounts to identify the amount of funding that is unobligated. On behalf of American taxpayers, OMB has an obligation to ensure their money is being used wisely.”

Trump has proposed steep cuts in foreign aid in all of his budget requests, but Congress has restored the funding.

Last year, OMB asked the State Department and USAID to provide a similar balance sheet of unobligated projects just six weeks before the end of the budget year. It said money for projects considered “unnecessary” — potentially as much as $3 billion — could be returned to the Treasury, a process known as rescission

Secretary of State Mike Pompeo argued against the rescission championed by OMB Director Mick Mulvaney, and Congress pushed against what it viewed as a backdoor attempt to get around its spending authority, so the administration dropped the proposal. The Government Accountability Office, in a decision last December, rebuked the idea of an attempted rescission so late in the budget year, saying there must be enough time for a “prudent obligation” that could take weeks or even months. This year, Pompeo was in Australia when the letter was sent and Congress was near the beginning of a recess.

No decisions have been made, and the information requested from the agencies is purely for the purpose of review. But the memory of the failed attempt to slash foreign aid last year has led some in the broader foreign aid community to be concerned that Mulvaney, who remains head of OMB and is the acting White House chief of staff, will try again.

“He’s tried again and again to take a sledgehammer to the most minuscule yet high impact part of the budget,” said Liz Schrayer, president of the U.S. Global Leadership Coalition, a network of businesses and organizations that advocate for international development. “He keeps losing, because Congress has seen in a bipartisan fashion these cuts are reckless, and these funds are in America’s security interest. I think we’ll see that again.”

A senior Democratic aide said that it appears the administration is preparing to circumvent Congress with a rescission package and that it can expect a fight.

“Irrelevant of what the Trump administration may wish, Congress still has the power of the purse and we appropriated these funds because they are necessary to protect our interests and national security,” said the aide, who like others spoke on the condition of anonymity to discuss plans under consideration. “We are in touch with the State Department and are demanding answers. This scheme would set the precedent for this and all future administrations to ignore spending bills and eliminate spending obligations by jamming Congress with end-of-fiscal year rescission packages.