As a new school year begins for the Pittsburgh Public Schools, a labor dispute is threatening to disrupt operations for the second year in a row.

Clerical workers represented by Local 2924 of the American Federation of State, County and Municipal Employees last night nearly unanimously authorized their negotiating committee to call a strike at any time.

The 163-2 vote, at Pittsburgh Federation of Teachers offices on the South Side, came after union leaders gave an update on contract talks.

Custodians, truck drivers, food-service workers, mechanics and other workers represented by AFSCME Local 297 will meet at 9 a.m. Saturday at Pittsburgh Carrick High School to discuss talks and take a strike authorization vote. Local 297 authorized a strike last school year, but remained on the job.

Richard Caponi, director of AFSCME District Council 84, Downtown, said the locals together represent about 500 employees. The school district Web site says the locals together represent about 550 workers.

The locals' last contracts expired in December 2006. Mr. Caponi said each local has talked with the district within the past three weeks.

Despite his decision to seek strike authorization, Mr. Caponi said he remained committed to negotiating a contract without a work stoppage.

He said stumbling blocks include the district's proposals for "multiple years of wage freezes" and a change in language that would make it easier for the district to furlough workers.

School board member Theresa Colaizzi, chairwoman of the district negotiating committee, said AFSCME did not inform the district of the strike authorization votes and she feared the union was making a "play to disrupt" the start of the school year.

Ms. Colaizzi also said she was disappointed to hear that the union is contemplating a strike because negotiating sessions are scheduled for Monday and Sept. 2. She said she wondered whether the union negotiators will attend those sessions committed to getting the work done.

Last fall, though the AFSCME workers were without contracts, it was the district's dispute with the teachers union that took center stage.

Teachers and other employees voted in October to authorize a strike, but the union leadership didn't call one. Agreements with teachers and other professional employees were reached in January, and agreements with two smaller bargaining units representing technical-clerical workers and paraprofessionals were reached in June.

Ms. Colaizzi expressed frustration with the pace of the AFSCME talks as far back as March. The parties talked for 18 hours straight March 3-4.