A nonpartisan budget group is raising concerns that New York City taxpayers could be on the hook for a bulk of the $1 billion the city is projecting to spend as a result of the migrant crisis.

Since the spring, more than 23,000 asylum-seekers have been bused to New York City from southern border states as part of a political tactic by political leaders there.

City officials have maintained they are eligible for federal reimbursement funds that cover emergency shelter contracts, a tent encampment built on Randall’s Island that is set to close this week and other services. The $1 billion estimate is a conservative projection the city says is spread across agencies responding to the crisis, including the Department of Social Services, Office of Emergency Management and the city's public hospital system.

The city didn’t provide a specific breakdown of costs.

The Independent Budget Office said the city needs to provide more detail about its reimbursement strategy with the federal government, which has a limited number of programs that can fund such expenses. In some cases, Congress or the Biden administration may need to intervene to approve funding requests over certain amounts.

“The source of those funds have not yet been identified,” said Beth Brown, the IBO’s communications director. “We don’t have a clear indication that those funds would be available.”

The IBO has estimated that the cost of caring for the migrants is at least $600 million based on the total number of asylum-seekers who’ve arrived in the city so far.

On Monday, Mayor Eric Adams said that now that “the campaign season is over,” elected officials should attend to the city’s financial needs.

“We need to be reimbursed. We spent a great deal of money for a national problem, and we are looking for reimbursement and assistance from the state and from the federal government,” he said.

"Our compassion is limitless, but our resources are not, and we must meet our legal obligation to provide shelter," said Jonah Allon, a spokesperson for the mayor.

"We have already begun engaging with the federal government on reimbursement, to defray the costs the city has incurred in providing shelter, food, and services to asylum-seekers," Allon said. "We remain confident that the federal government will recognize the city’s fiscal needs and provide us with the necessary resources.”

The IBO’s worries come as city budget analysts released its so-called November plan, which modifies the city’s existing budget based on incoming revenues. The Office of Management and Budget, charged with balancing the budget, found the city will save $2.5 billion over the next two years based on agency savings.

During a budget briefing on Tuesday, officials with the OMB said they were in the midst of drafting a letter to the federal government and examining different grant options.

It comes two months after the OMB ordered across-the-board agency cuts framed by the Adams administration as an attempt to offset a looming fiscal crisis. The so-called Program to Eliminate the Gap, or PEG, ordered city agencies to make a 3% reduction in agency spending this fiscal year and 4.75% in cuts the next fiscal year.

This story has been updated to include comment from the mayor's office.