Hundreds of Internal Revenue Service employees have received permission to skip work during the partial government shutdown due to financial hardship, and union leaders said Tuesday they expect that number to surge as part of a coordinated protest that could hamper the government’s ability to process taxpayer refunds on time.

The Trump administration last week ordered at least 30,000 IRS workers back to their offices, where they have been working to process refunds without pay. It was one of the biggest steps the government has taken to mitigate the shutdown’s impact on Americans’ lives.

But IRS employees across the country — some in coordinated protest, others out of financial necessity — won’t be clocking in, according to Tony Reardon, president of the National Treasury Employees Union, and several local union officials.

The move is the leading edge of pushback from within the IRS, and it signals the potential for civil servants to take actions that could slow or cripple government functions as the shutdown’s political stalemate continues in Washington. U.S. Department of Agriculture meat inspectors have begun to call in sick, Transportation Security Administration sickouts at airports have been rising, and federal law enforcement agencies say the shutdown is increasing stress among agents and affecting investigations.

“They are definitely angry that they’re not getting paid, and maybe some of them are angry enough to express their anger this way,” said Reardon, whose union represents 150,000 employees at 33 federal agencies and departments. “But these employees live paycheck to paycheck, and they can’t scrape up the dollars to get to work or pay for child care.”

Not receiving pay for more than a month has taken a toll on employees across the government, but especially on those who are not in high-salary jobs. The employees summoned back from furlough to process tax refunds are paid between $25,800 and $51,000 a year, depending on their seniority. IRS employees will miss a second paycheck Monday if the government does not reopen this week.

“I’m at the point where I cannot afford to go to work,” said Marissa Scott, 31, an IRS customer service representative who is out on hardship leave. Scott lives outside Kansas City, Mo., and drives 98 miles round trip to work each day. “I cannot afford to fill my gas tank.”

Scott, who has worked at the IRS for four years, says she typically helps as many as 50 people a day with their returns during tax season, including U.S. troops stationed overseas. She said the shutdown could delay refunds for months, and without employees like her on the job, “it’s going to be a disaster all around.”

Many of the IRS employees who are choosing not to come to work despite getting called back are taking advantage of a provision in the union contract that allows them to miss work if they suffer a “hardship” during a shutdown, according to the labor groups.

That could mean a blown car tire, an empty gas tank or a child-care bill.

Duncan Giles, who has worked for 24 years at an IRS call center in Indianapolis, said more workers are requesting hardship leave as they learn it exists.

“The more this goes on and the tougher it is to get to work — they simply cannot afford it,” said Giles, president of NTEU Chapter 49. “Every single person wants to be at work. They want to help the American taxpayer. But we have to pay for gas and child care.”