Senators agreed to the amendment, introduced by Sens. John Kerry, D-Mass., and Olympia Snowe, R-Maine, by unanimous consent, before completing the spending bill.
The language would require TSA to follow rules set out in the Federal Acquisition Regulation, which apply to almost all federal agencies.
"Why should an agency fraught with wasteful spending and contract mismanagement continue to receive a free ride while every other major federal agency must abide by the law?" Kerry said in a statement. "The taxpayers deserve better. Our small businesses deserve better. This change to bring transparency and accountability to the TSA is long overdue."
Kerry is the chairman of the Small Business Committee; Snowe is the ranking member.
The Senate passed an identical amendment last year during consideration of the fiscal 2007 Homeland Security appropriations bill, but the provision was removed in conference negotiations with the House. Kerry spokeswoman Kathryn Seck said the amendment has a better chance this year because the Democrats control Congress.
"The language was stripped out in conference by the Republicans last year," Seck said. "There's no reason for this to not go forward other than Republican obstructionism, and Senator Kerry is certainly going to work to keep it in."
John Gentzel, press secretary for Snowe, said she also is working hard to ensure the amendment remains part of the spending bill.
TSA has been exempt from governmentwide acquisition rules since its inception in November 2001, to allow the agency to quickly install security screening equipment at airports after Sept. 11.
The Professional Services Council, an association representing contractors, has endorsed the amendment, saying it would help standardize procurement processes, increase competition and expand opportunities for small businesses.
As the TSA language heads toward the stage at which it was killed last year, the future of the spending bill as a whole remains unclear. The Senate's version has about $3 billion more in total spending than the House's version. It also surpasses President Bush's request by $5.3 billion. Bush has vowed to veto any spending bill that exceeds his request.