Health workers warned today that patients at five hospitals in north-west England face more infections if bosses order porters to carry out cleaning duties.
University Hospital of Morecambe Bay Foundation Trust bosses are proposing to change porters' job descriptions to include "terminal cleans," GMB said.
These are deep cleaning operations of specific areas - including ones where there have been particular problems, such as highly-infectious and deadly MRSA.
Over 350 deaths in England and Wales were linked to MRSA in 2011.
GMB said that porters will be expected to carry out their normal duties at the same time, which include lifting and moving patients - putting them at greater risk of infection.
Northern regional organiser Steve Gibbons said: "Terminal cleaning is what happens when there has been an infection, and they want a deep clean.
"At the moment it is a separate job from portering. Management say it will hardly ever happen but once you mix the roles it becomes part of the job.
"The trust has faced a number of issues over the last couple of years and has many more to face.
"Forcing staff to change their roles in an ill-thought-out way does not fill the GMB with confidence that the trust is up to the challenges ahead."
Bosses also plan to rename porters "patient environmental assistants."
The trust runs Furness General Hospital, Royal Lancaster Infirmary, Westmorland General Hospital, Queen Victoria Hospital in Morecambe and Ulverston Community Health Centre.
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