FedEx, which began as an airline, is governed by the Railroad Labor Act, which permits unions on a national basis only, The Hill newspaper reported.

FedEx rival UPS is governed by the National Labor Relations Act, which allows for local unions.

FedEx was switched to NLRA rules for one year, but the Federal Aviation Administration reauthorization bill under consideration in the Senate would allow FedEx return to its RLA status.

UPS has been quiet in the issue, but labor groups have called it a "sweetheart deal" The Hill reported.

At least one Senator is opposed to ending FedEx's exemption.

House Transportation and Infrastructure Committee Chairman Jim Oberstar, D-Minn. "is committed to it," legislative director for the Teamsters Fred McLuckie said.

McLuckie, however, expects an effort to insert FedEx language in the reauthorization bill would derail its passage. He expects unions will make a stronger stand on the issue later this year, he said..