Workers at the Mid Yorkshire NHS Hospitals Trust will take industrial action next month.
The trust, which runs Pinderfields, Pontefract and Dewsbury hospitals, wants to transfer the contracts of cleaners, canteen staff, IT staff and maintenance workers to a separate company.
It means that they would lose NHS terms and conditions, and their contracts could be sold to a private firm.
Unions say this would create a “two-tier workforce” and have branded the plans an “insult” to staff. The trust said they wanted to work with unions and had not yet received permission from the Government to go ahead with the plans.
More than 97 per cent of those balloted voted in favour of striking. There was a turnout of 58 per cent.
Unison said the strike would take place Monday July 2.
Adrian O’Malley, regional branch secretary of Unison, said the result had sent a “clear message” to the trust’s management. He said: “Members are really angry and to say to these people that they won’t be part of the NHS is an insult. They don’t work in hotels. The work that they do has a direct impact on patient care.
Jules Preston, chairman of the Trust said: “I can confirm that we have received the results of the ballot from Unison and that its members have voted in favour of pursuing strike action. We have invited the unions to work with us – with the first meeting having taken place on June 12 – to explore the various options available to us from a staffing model point of view.”