Here are the reasons more federal workers are still showing up for work despite not getting paid.

The law prohibits them from striking

The National Labor Relations Act extends a right to strike to American workers — but it specifically does not give that right to government workers. A law passed during President Jimmy Carter’s administration bars federal workers from striking. When air traffic controllers walked off the job in 1981, demanding better pay and working conditions, President Ronald Reagan ordered them to return to work. When they did not, he fired them.

For an employee deemed “excepted” from furlough during a shutdown — which is to say, forced to work without pay — walking off the job could carry a similar penalty. Guidance from the federal Office of Personnel Management prohibits excepted employees from taking any sort of leave, including vacation or sick days, during a shutdown.

“If an excepted employee refuses to report for work after being ordered to do so,” the guidance says, “he or she will be considered to be absent without leave (AWOL) and will be subject to any consequences that may follow from being AWOL.”

Employees believe in their mission

Union leaders and federal workers frequently stress that furloughed employees want to be allowed to return to their jobs — and that employees working without pay are doing so largely because they care about their work, be it protecting public lands, inspecting food for safety or catching drug smugglers at the border.

“It sounds corny, I know,” said Jacqueline Simon, the director of public policy for the American Federation of Government Employees, the largest federal workers’ union. But “federal employees are extremely devoted to the mission of their agencies,” she said. “They don’t just fall into these jobs. They believe in public service; they believe in what they do. They’re not just going to walk away. There may come a point when some of them have to, to feed their families, but no one wants to do that.”