North Yorkshire County Council is using a new national agreement for public-sector workers to drive through an increase in hours for nursery nurses. Classroom assistants are also affected.
They would switch from a 32-and-a-half hour week to 37 hours for the same salary and lose their holiday pay. Staff calculate it will cost them up to pound;3,000 a year to work the same hours.
They are covered by the Single Status Agreement hammered out two years ago nationally by unions and local government to update terms and conditions for blue-collar and white-collar council staff. It was intended to usher in a peaceful era in industrial relations under a Labour Government and in most places it has been implemented without problems.
The deal means that from April 1 manual workers will switch from a 39-hour week to the 37 hours enjoyed by white-collar colleagues with no loss of pay. Playground supervisors are among those who will benefit.
North Yorkshire says the pay rise will cost it pound;2.27 million and warned staff that it would "seriously threaten the survival of some important services".
Unison, the public-sector union, accuses the council of trying to recoup the costs through a pay cut for nursery nurses and classroom assistants.
Branch officer Rosie Kett said: "The county council has known for two years that the 37-hour week was coming. Our view is they should have been making preparations earlier."
Unison is keeping a close eye on the case. Kate Foley, national officer for nursery nurses, said: "We're not aware that these proposals are being replicated elsewhere, and we would be very concerned if they were."
A three-month consultation period has already ended, but Unison said it was prepared to talk further before going to arbitration. North Yorkshire Council said it was unable to comment further while talks continued with the union.