WASHINGTON — The largest union for federal workers urged Congress on Monday to pass a “clean” funding bill to end the government shutdown, undercutting Democrats who are demanding that any deal include subsidies for people who get their insurance through the Affordable Care Act.

The move by the American Federation of Government Employees, which is typically a Democratic ally, underscores the difficult spot federal unions find themselves in. Nearly four weeks into the shutdown, hundreds of thousands of workers are furloughed and missing paychecks, while some face the possibility of further layoffs by the Trump administration.

Everett Kelly, AFGE’s president, said in a statement that it is time to “put every single federal worker back on the job with full back pay.”

“Both political parties have made their point, and still there is no clear end in sight,” Kelley said.

The union’s new position, first reported by NBC, could put added pressure on Democrats to vote to end the shutdown after a monthlong stalemate over government funding in the GOP-controlled Senate. Republicans quickly seized on it to call on Democrats to back down.