The Westchester County executive says he’ll have to lay off 126 workers, mostly in social services, to balance next year’s budget.

County Executive Robert Astorino says the layoffs wouldn’t be necessary if workers in Westchester’s largest union had agreed to contribute to health care costs. The union says it’s still negotiating.

Astorino’s $1.72 billion proposal sticks to his no-tax-increase pledge for a third year. He said Wednesday the layoffs are necessary to offset the increased costs of salaries, health care, pensions and Medicaid.

Astorino’s budget would cut funding for three neighborhood health centers and increase the amount parents would pay for day care.

He also proposes borrowing to cover some pension costs and the costs of court-ordered tax reductions.

The county Legislature has until Dec. 27 to adopt a budget.