Hundreds of health workers are to strike on Wednesday in a dispute over outsourcing of services.
Members of Unite at the Wrightington, Wigan and Leigh Foundation Trust will walk out one minute past midnight while Unison members will strike from Thursday.
Workers including porters, cleaners, catering staff, electricians and plumbers employed at Wrightington Hospital, Wigan's Royal Albert Edward Infirmary and Leigh Infirmary will take action.
The trust is proposing that the workers' jobs will be outsourced to a subsidiary company, WWL Solutions Ltd.
Unite members will strike for 24 hours tomorrow followed by five days of strike action by both unions from Thursday.
Unite regional officer Keith Hutson said: "These loyal and dedicated workers undertake a crucial role in keeping hospitals open and properly functioning. They are a core part of the NHS family and their jobs should not be hived off."
Unison general secretary Dave Prentis said: "There's no good reason for this outsourcing - it's bad for patients and bad for the staff that support them.
"As the NHS approaches its 70th birthday, it deserves better than being salami-sliced into different organisations. The NHS is the envy of the world, but it won't stay that way by breaking up its staff and services."
A Trust statement said: "We would like to reassure our patients, staff and the public that business continuity plans are being carried out to ensure that our services will continue to run as smoothly and safely as possible during the six days of industrial action.
"However, some disruption to services is likely. Shops and dining rooms will be closed on all sites, but there will be general catering provisions available in vending machines and snack trollies will be made available for staff, patients and visitors.
"Should treatment be required, we would encourage, where possible, patients to think about using alternative services such as GPs, walk-in centres, 111, and pharmacies unless life threatening or in an emergency."
The Trust's board will discuss setting up a wholly owned subsidiary at a meeting tomorrow afternoon.