By: DONNA BORAK, CNN

(CNN) – The Internal Revenue Service is recalling tens of thousands of additional federal employees with less than two weeks before tax filing season begins.

The federal tax collector said Tuesday in an undated government shutdown plan it would call back an additional 36,000 federal employees, bringing the total number of those working at the IRS during the government shutdown to more than 46,000, or roughly 57 percent of the workforce.

The move will allow Americans to get their tax refunds on time, but at the expense of the IRS employees, most of whom won’t be paid.

Only 809 federal employees in two specific areas of the agency will get their paychecks because their operations are funded by user fees.

The National Treasury Employees Union, which represents roughly 70,000 IRS workers around the country, said Tuesday that the executive branch can’t continue to force more and more employee to show up in exchange for an IOU.

“There is no doubt the IRS needs to get ready for the 2019 filing season that starts January 28, and IRS employees want to work,” union president Tony 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.”

This year’s tax filing season begins on January 28.

The IRS is part of Treasury, one of the federal agencies affected by the government shutdown that’s now in its 25th day. Since the shutdown, it has been operating with only 12.5 percent of its workforce, or fewer than 10,000 employees.

Earlier this month, the Office of Management Budget reversed a long-standing policy that refunds due to individuals and corporations would go unpaid during a shutdown, saying “tax refunds will go out.”

Earlier this month, the union asked a federal judge to immediately stop the federal government from continuing to require employees to work without pay.

It’s an open question whether recalled workers will be able to claim unemployment insurance since the laws vary state by state. Federal employees in California who have been furloughed or who are continuing to work but don’t collect a paycheck, are eligible to claim unemployment benefits, according to the state’s employment office.