Staff at Bradford hospitals have voted to take strike action over plans to set up a new company to run the facilities.
Bradford Teaching Hospital Trust wants to transfer workers such as porters and cleaners to a subsidiary company.
It said "patient safety and levels of care" would not be hit "by any industrial action".
Natalie Ratcliffe, of the Unison union, said: "Our members are very angry. We want them to scrap the plans."
Some 97% of votes cast by members were in favour of strike action at Bradford Royal Infirmary, St Luke's, and Shipley Hospitals, and three community hospitals at Eccleshill, West Wood Park and Westbourne Green.
A walkout involving more than 300 members, lasting up to seven days, could start in July, the union said.