White House officials made clear on Tuesday that President Bush was prepared to veto a bill that enacted recommendations of the Sept. 11 Commission if the provision granting Transportation Security Administration workers collective bargaining rights was not removed.
"Existing authority permits T.S.A. the flexibility to manage and deploy their work force," Scott Stanzel, the White House deputy press secretary, said. "We do think that it is important that T.S.A. maintain that flexibility for personnel performing key homeland security roles."
In a letter sent Tuesday to the White House, Senator Jim DeMint, Republican of South Carolina, and 35 other Senate Republicans said they were prepared, if necessary, to sustain a veto.
Security administration officers are already allowed to join a union. But few do, as current federal law does not permit the union to bargain on their behalf to contest workplace assignments, file grievances or represent them in disciplinary matters. Backers of the measure say giving the T.S.A. workers broader rights does not create security problems.
"There’s no good reason to deny these rights to these people," Senator Joseph I. Lieberman, independent of Connecticut, said Tuesday, as the Senate took up the matter.
What collective bargaining rights Department of Homeland Security employees should have has been under dispute since shortly after the 2001 attacks.
The disagreement so divided Congress in 2002 that for months it prevented passage of the bill to create the department. Republicans successfully used the delay, for which they blamed Democrats, to help defeat Senator Max Cleland, the incumbent Democrat of Georgia, that year, openly questioning his commitment to fight terrorism.
Republicans ultimately prevailed, both with T.S.A., which initially was part of the Department of Transportation, and with Homeland Security, which has since taken over.
But union leaders have been pushing ever since to reassert bargaining rights for department employees.
Union leaders say airport screeners are frequently required to work unscheduled overtime, suffer high injury and illness rates - nearly 30 percent compared with 5 percent for all federal employees - and have an attrition rate 10 times as high as the federal average.
"How safe is the public if officers who see security breaches that result from mismanagement cannot disclose that because they fear they could be fired?" said Mark D. Roth of the American Federation of Government Employees.
Under the proposal, the security officers would not have the right to strike, and the union would not have the power to negotiate wages. But it would be authorized to bargain on their behalf to establish work rules to govern overtime and temporary transfers, and to protect them if they file a grievance.
Union officials said that T.S.A., under the proposal, would still have the power, in emergencies, to change work assignments. But Kip Hawley, the security agency’s administrator, said such shifts were necessary not just in emergencies but when routine events like weather delays required work reassignments or overtime.
"We require an infinitely flexible security regime that allows us to change what we do and where we do it," Mr. Hawley said, adding that hiring staff members to handle union relations would cost $160 million.
The debate over the collective bargaining rights is just one of several points of contention expected to surface as the Senate takes up its version of the Sept. 11 Commission bill. House Democrats passed their own version in January.
House Democrats, who also included a provision granting collective bargaining rights to airport screeners, have language in their bill that would mandate inspection of all ship containers headed to the United States from overseas, a provision that the Bush administration and many Republicans oppose. A push by Democrats is expected in the coming week to add such language to the Senate bill.
The Senate bill is also likely to include measures intended to increase rail and transit security. And there may be an effort, also opposed by the Bush administration, to delay a 2008 mandate that the states begin to issue a standardized, tamper-proof driver’s license.
Officials in many states have said they will not be ready in time and that the federal government should cover the cost of issuing the new licenses.