Dozens of school districts are waiting on the outcome of a labor dispute between a private bus service and drivers in Belmont, who have threatened to strike and called on others to join in a work stoppage.

Members of Teamsters Union Local 633 authorized a strike Monday night, but are holding off on action pending a meeting today between the union and First Student, an Ohio-based company that contracts with school districts across New Hampshire.

Chris Kemper, a spokesman for First Student, said Tuesday a clause in employee contracts prohibit workers who have an unexpired contract in place from going on strike.

That would mean only workers whose contracts have expired – like workers at the company’s Belmont location – can strike. That location serves school districts in Laconia, Gilford, Gilmanton, Alton, and the Shaker Regional School District in Belmont, which includes Canterbury Elementary. All other union contracts with First Student districts in the state are active, Kemper said.

“Our expectation is that both sides will deliver on the agreement as we planned it,” he said.

But the union has told media that striking workers could set up picket lines at First Student facilities across the state, effectively stopping work there too, and school districts are bracing themselves accordingly.

“They might also decide to set up picket lines at other First Student New Hampshire bus terminals, including the one in Derry,” Derry Cooperative School District Superintendent Laura Nelson told parents in a letter sent home Monday. “If they do so, our drivers will not cross the picket line.”

In Hopkinton, where between 400 and 600 students rely on the bus to get to school, Superintendent Steve Chamberlin warned building administrators to prepare over the weekend. He said Tuesday he hadn’t heard from the union or the company about what could happen, and was waiting for the outcome of today’s meeting between the two parties.

Chamberlin said he had also been in contact with administrators in Hillsboro, Deering and Andover, who also contract with First Student.

At issue in the dispute are retirement benefits. Union officials have claimed First Student hasn’t been making good on pension contributions. Meanwhile, Kemper said the union wants to participate in a pension plan the U.S. Treasury Department has said is so underfunded it’s “endangered.”

“We believe that participation in the plan is not in the best interest of our employees or the districts that we serve,” he said.

Someone from Teamsters 633 was not available to answer questions from the Monitor on Tuesday.

(Lola Duffort can be reached at 369-3321 or lduffort@cmonitor.com.)