From the Washington Post:

The Internal Revenue Service and its roughly 90,000 employees had expected to weather the impending government shutdown by staying open for business, thanks to the $80 billion boost provided by the Inflation Reduction Act.

But that abruptly changed this week.

On Thursday, the tax agency released an updated contingency plan showing that it will furlough up to two-thirds of its workforce — 60,000 employees — if the government comes to a halt on Sunday, a move that will affect vital services to taxpayers as late-filing season closes out.

The agency’s whiplash was prompted by late guidance from federal officials that IRS could not, in fact, cover workers’ salaries during a shutdown with funds from President Biden’s landmark climate change, health care and tax law.

Although the IRS had held for months that it could do business as usual if government funding lapsed, the Office of Management and Budget told the agency this week that the money cannot substitute for the agency’s regular budget, which pays the salaries of most of its employees. The result will be a return to the backlogs at all levels of service that had begun to disappear in the last year, current and former IRS officials said.

https://www.washingtonpost.com/politics/2023/09/28/irs-shutdown-furlough-inflation-act/  (may be paywall protected)