A bitter battle over a simple issue — how long truck drivers should be allowed for bathroom and meal breaks — was renewed on Capitol Hill on Thursday and may be the death knell for a vital House bill to fund aviation.

The overall bill has nothing to do with truckers. Instead, it is a six-year reauthorization for the Federal Aviation Administration. The provision about truckers is tucked in on page 256 in a welter of legal jargon that makes no actual mention of trucks, truckers or trucking. It just prohibits states from regulating the “hours of service” of certain workers who are regulated by the U.S. Department of Transportation.

In other words: truckers.

Twenty-two states have laws that give truckers more frequent or longer bathroom and meal breaks than current federal regulations, which stipulate that truckers take a minimum 30-minute break eight hours after they climb behind the wheel.

[House Republicans move ahead with plan to shift 38,000 FAA workers]

“I think that if your employer told you that you would get docked [in pay] when you go to the bathroom or have a meal break, I think you would be outraged, too,” Sen. Barbara Boxer (D-Calif.) told reporters Thursday. “This terrible anti-safety, anti-worker provision is a poison pill that has no place in an FAA bill.”

Boxer sent a letter to the leaders of the Senate Commerce Committee, John Thune (R-S.D.) and Bill Nelson (D-Fla.), urging them to drop the trucking provision if they undertake to introduce a Senate version of the FAA bill.

The backdrop for the battle Boxer renewed Thursday is intriguing. The trucker provision originally was more suitably placed in the highway bill that Congress approved last year. Boxer was unalterably opposed to it.

One evening, as aides recount it, she had a severely unpleasant telephone conversation about it with House Transportation Committee Chairman Bill Shuster (R-Pa.). The call did not end well, and staff members were left to pick up the pieces the next morning. The trucker provision was withdrawn from the highway bill, only to resurface this year in the FAA bill.

State provisions allowing truck drivers more rest have been unsuccessfully challenged in court by the trucking industry. The American Trucking Associations says that truckers are allowed to take breaks whenever they become too tired to drive.

The International Brotherhood of Teamsters opposes the congressional effort to override state rest regulations. Teamsters President James P. Hoffa said in a statement: “These elected officials are doing the bidding of the American Trucking Associations, which wants drivers on the clock as much as possible.”

Shuster is the third-leading recipient of trucking industry campaign contributions. He has received $321,641 over a career that started with his election in 2001. During the 2014 election cycle, the trucking industry contributed more than $2.5 million to candidates from both parties, according to federal campaign reports compiled by the Center for Responsive Politics.

Shuster did not respond to a request for comment Thursday.

Authorization for the FAA expires March 31, and Congress is expected to extend the current authorization bill before that date. The big debate may focus on a House proposal that would spin off about 38,000 FAA workers and a $40 billion project to a private, nonprofit corporation run by the airlines and other industry stakeholders.

But Boxer, without mentioning her late-night call with Shuster, pointed out Thursday that the trucker provision was among the last issues resolved before the highway bill passed.

“And I said, ‘No way on my watch is that going to happen,’ ” Boxer said.

One Republican House aide said Thursday, “And even in the House, the votes just aren’t there to pass anything like the bill Shuster got through committee earlier this month.”