A yearslong effort to expand the rights of women to pump breast milk at work has been held up near the finish line due to opposition from the airline industry, according to a senator involved in the fight.

The bipartisan bill ― known as the Providing Urgent Maternal Protections for Nursing Mothers Act, or PUMP Act ― would guarantee more U.S. workers the time and space to express breast milk while on the job. The legislation already passed the House but hit roadblocks in the Senate, where Democrats need to secure more GOP support.

Sen. Jeff Merkley (D-Oregon), who co-sponsored the bill with Republican Sen. Lisa Murkowski (Alaska), told HuffPost that some senators are holding up the legislation due to resistance from the airlines. He said Senate staff have worked on language in the bill to accommodate the industry, but the airlines are still opposed.

“For months, we have worked tirelessly in good faith to address every concern they have over costs and safety,” Merkley said in a statement. “These are the same airlines that say they are greatly concerned about the health and welfare of their workers. Yet they are blocking the ability of their workers to pump breast milk at work.”

“Not only are they blocking this for their employees, but they are blocking it for 9 million other workers across the country,” the senator added.

The Affordable Care Act of 2010, known colloquially as Obamacare, set a new requirement for employers to provide workers with a clean, private space and reasonable break time to pump milk for their babies. But because the rule was tied to minimum wage and overtime law, it excluded millions of workers who are salaried employees ― a carve-out the PUMP Act is meant to end.

Both the rail and airline industries said they had problems with the PUMP Act, arguing their unique working environments needed special attention. The bill’s backers reached an agreement with rail representatives to allay their concerns, but haven’t managed to do so with the airlines, which are seeking special language related to flight attendants and pilots.

The latest version of the bill would not allow workers to pump during critical flight periods, including takeoff and landing, which backers of the bill hoped would end the standoff. It would also allow air carriers to comply with the law by simply hanging a curtain for privacy, to avoid having to retrofit airplanes.

But the industry is also seeking language guaranteeing that any state laws related to breast pumping would be preempted and not apply to them.

Delta, United and American Airlines all declined to comment when asked if they support the PUMP Act, referring HuffPost to an industry trade lobby, Airlines for America.

A spokesperson for the group said in a statement that airlines “already voluntarily” provide time and accommodations to pump, and insisted that “in-flight crew duties are inherently unique.”

“As safety is and always will be our top priority, we continue to advocate for a consistent federal standard for our in-flight crews that keeps them and our passengers safe,” the group said.

Sara Nelson, president of the Association of Flight Attendants-CWA union, said the industry seeking a preemption from state laws was a “delay tactic.” She called the airlines’ opposition “disgusting” and said they were trying to “hide behind” their trade group.

“At this point, it’s about killing it,” Nelson said. “Any airline that says they support the right of women to pump in aviation is lying because they’re not telling these Republicans to stand down.”

Democrats and many Republicans agree that making sure breastfeeding mothers can pump at work is a commonsense, family-friendly policy. But it’s also about basic dignity and health on the job. Not being able to pump when necessary can lead to serious pain and infection.

A 2019 HuffPost investigation documented workers who developed mastitis after their employers put up barriers to them pumping at work. Many companies are still reluctant to set up devoted pumping areas or provide workers with breaks, even for those who are covered by the law.

Nelson said flight crews need to be included in the law because “it’s physically impossible most days to pump around your flights.” Even if some airlines voluntarily accommodate pumping now, Nelson said airline crews need guarantees under the law like other workers.

“I’ve done this. It’s really hard,” she said. “Flight attendants make it work today, but guess what? There are no rules around it.”

The current window to get the bill into law is running short, since Democrats lose their House majority when the new Congress is sworn in next month. The best shot at passing the law may be to include it in an omnibus spending package before Christmas, if the measure gains enough support.

Dozens of House Republicans voted in favor of the PUMP Act when it passed in October 2021, but lawmakers would have to approve another version under GOP leadership if backers can’t get it over the finish line this year. The bill is unlikely to be the same priority in a Republican House.

One lawmaker who opposes the legislation, Republican Sen. Roger Wicker of Mississippi, declined to explain his concerns when asked by HuffPost. He acknowledged there had been “staff to staff” discussions about the airlines’ issues.

“I don’t think it’s going to fly,” Wicker said of the bill.

Igor Bobic provided additional reporting.