The IRS plans to call about 45,000 furloughed employees back to work in order to issue tax refunds, according to the union representing agency employees.

Nearly 70,000 Internal Revenue Service employees—about 87.5 percent of the agency’s workforce—haven’t been able to work since the partial government shutdown began in December. The employees who remained at work were tasked with implementing the 2017 tax law, conducting criminal investigations, and handling information technology issues.

The tax filing season is scheduled to begin on Jan. 28, whether or not the partial government shutdown is resolved. The White House Office of Management and Budget said earlier in January that the IRS will be allowed to process tax refunds, a departure from how previous administrations interpreted the law regarding what is and isn’t allowed during a government funding lapse.

That plan will require about 45,000 employees to return to work without pay, according to a Jan. 13 court filing from the National Treasury Employees Union. The union, which represents workers at the IRS, Environmental Protection Agency, and other federal agencies, sued over the government forcing some union members to work without pay during the shutdown.

The IRS didn’t immediately return a request for comment.

The U.S. District Court for the District of Columbia will hold a Jan. 15 hearing on a motion by the union, which is seeking a temporary restraining order that would prohibit the federal government from requiring employees to work without pay during a funding lapse.