Sen. Barbara Boxer (D-Calif.) vowed today to block a measure included in an aviation reform bill to pre-empt states from imposing their own rules on meal and rest breaks for truck drivers, calling the language a threat to highway safety and an effort by big trucking firms to take economic advantage of drivers by keeping them behind the wheel for as long as possible.

Boxer, ranking member of the Senate Environment and Public Works Committee, who is retiring when her current term expires in January, said the measure, which earlier this month passed the House Transportation and Infrastructure Committee, has no place in any bill before Congress. Boxer told a press briefing in Washington that she wrote Sen. John Thune (R-S.D.), chairman of the Senate Commerce Committee, which oversees aviation legislation, and Sen. Bill Nelson (D-Fla.), the committee's ranking member, to block the provision from being included in the Senate's version of legislation to reauthorize funding for the Federal Aviation Administration.

The House measure—known as "Section 611"—would grant federal pre-emption power over what remains of state economic regulations of interstate trucking services. The measure, which was excluded from the federal transport-spending bill that became law in December, was in response to a 2014 ruling by the 9th U.S. Circuit Court of Appeals upholding California's driver meal and rest time rules as not subject to federal pre-emption because the state's policies did not bind motor carriers to specific rates, routes, and services, and thus did not interfere with competitive market forces. The U.S. Supreme Court declined to hear an appeal of the ruling, and after the language was dropped from the federal spending law, advocates successfully lobbied to include it in the aviation bill.

Critics of the measure, which include the Teamsters, independent owner-operator drivers, and safety groups, said it prevents states from ensuring that drivers get paid for their break times, as well as for nondriving work like loading and unloading their trucks. Though the language is aimed at overturning the court's ruling on the California requirements, the practical effect would be to pre-empt regulations in 20 states and two territories, and "to any state that would move to protect their truck drivers," Boxer said.

Boxer added that drivers concerned about not being paid for nondriving time will feel compelled to spend more time behind the wheel, thus running the risk of being fatigued while operating a large vehicle.

Supporters of the measure said the language clarifies Congress' intent that the industry be governed by one set of federal rules covering driver break requirements. The Federal Motor Carrier Safety Administration (FMCSA), the unit of the Department of Transportation that regulates truck safety, requires that drivers take at least a 30-minute break during their first eight hours of driving. Supporters said the measure doesn't eliminate breaks for drivers, and said it creates no incentive for trucking firms to short-change their drivers by not paying them for breaks.

When Congress enacted legislation in 1994 pre-empting state regulations of interstate trucking, it didn't intend for carriers to change their driver-payment practices depending on what state they're driving in, supporters of the measure contend.