LOS ANGELES (AP) — Union officials say about 4,000 children's social workers for Los AngelesCounty have gone on strike after contract talks broke down over the timing of a pay raise and the number of caseloads the workers must handle.

Workers took to the picket lines Thursday in the first county strike in more than a decade. The strike was called Wednesday night by the Service Employees International Union Local 721. The union represents more than 55,000 county employees who have been working without a contract for more than two months.

The Los Angeles Times reports the two main obstacles in contractnegotiations are caseloads for social workers and the timing of a pay raise.