The Treasury Department on Tuesday released a shutdown contingency plan for the IRS during the tax-filing season, less than two weeks before the IRS will start processing tax returns.

Under the filing season plan, significantly more IRS employees will be working than have been during the first few weeks of the shutdown. While only 12.5 percent of the agency's roughly 80,000 employees were working under the nonfiling-season plan, 57.4 percent of the agency's workforce will be working under the filing season plan.

The plan has been eagerly awaited by lawmakers and tax professionals, who have expressed concerns that the funding lapse to the IRS could complicate the upcoming filing season — the first that reflects many of the changes made to the code by President Trump Donald John TrumpHR McMaster says president's policy to withdraw troops from Afghanistan is 'unwise' Cast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response MORE's tax law.

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Among those who will be called back to work are IRS employees involved in the payment of refunds. The IRS announced earlier this month that it will pay refunds during the shutdown, though in the past the agency had been directed not to pay refunds during a funding lapse.

Employees who respond to taxpayers' filing-season questions at call sites are also among those who will be working during the filing season, according to the contingency plan.

The tax-filing season will start on Jan. 28. In most states, the deadline to file tax returns will be April 15.

Tony Reardon — president of the National Treasury Employees Union (NTEU), which represents IRS employees — expressed concerns about the fact the IRS employees called back to work will not be paid while the shutdown persists.

“There is no doubt the IRS needs to get ready for the 2019 filing season that starts Jan. 28, and IRS employees want to work," Reardon said in a statement. "But the hard, cold reality is that they’ve already missed a paycheck and soon they’ll be asked to work for free for as long as the shutdown lasts.”

Earlier on Tuesday, a federal judge refused to issue an order sought by NTEU and the National Air Traffic Controllers Association that would have temporarily required the government to pay federal employees during the shutdown. The unions have also sought a preliminary injunction, and a hearing on that request is scheduled for Jan. 31.

--Updated at 4:06 p.m.