Hundreds of Internal Revenue Service workers dealing with financial hardship were given permission to miss work during the partial government shutdown, which could slow the federal government's ability to process taxpayer refunds, according to The Washington Post.
Union leaders told the newspaper they are expecting the absences to increase as part of a coordinated protest.
Last week, the Trump administration called back about 36,000 federal employees ahead of the tax filing season, bringing the total number of IRS employees working during the shutdown to about 57% of the workforce.
Many of the IRS employees who were called back are using a union contract provision that allows them to be absent from work if they suffer a "hardship" during a federal government shutdown, labor groups told the Post.
"They are definitely angry that they're not getting paid, and maybe some of them are angry enough to express their anger this way," Tony Reardon, president of the National Treasury Employees Union, told the Post. "But these employees live paycheck to paycheck, and they can't scrape up the dollars to get to work or pay for child care."
The National Treasury Employees Union could not provide the Post with an official number of absent workers and did not immediately respond to CNN's request for comment.
The IRS declined to tell the Post how many of its employees are out on hardship leave.
IRS spokesman Matt Leas told the Post that the agency is continuing its work to prepare for the beginning of tax-filing season, which begins on January 28.
"We are continuing our recall operations, and we continue to assess the situation at this time," Leas told the newspaper.