Another union has announced it will be supporting strike action at Wigan Infirmary and the borough's other health establishments later this month.
Stewards from Unite have signalled their members' unease over controversial plans to outsource Wrightington, Wigan and Leigh NHS Foundation Trust support roles to an arms-length third party.
Union leaders say 81 per cent voted in favour of striking, amid proposals to transfer hundreds of employees to WWL Solutions, a subsidiary company brought into being earlier this year.
Just under 60 per cent of eligible members of Unite, representing electricians, plumbers, fitters, porters and cleaners, turned out for the ballot.
Workers say they fear that the move by the hospitals trust would leave staff vulnerable to cuts to their pay, and terms and conditions.
Unite officials are calling for urgent talks with the trust in a bid to avert a walkout on May 23 and 24, when around 600 Unison members are also scheduled to strike.
Keith Hutson, Unite reigion said: "Our members, who keep our hospitals going, are angry at the way they are being treated.
"They are NHS employees, the same as any other hospital clinician, so why are they being side-lined?
"We will not stand by and watch this happen. They want their NHS jobs to stay in the NHS not to be privatised by transferring them to a subsidiary company.
"There is no reason to outsource these existing NHS jobs to WWL. The trust has a surplus of £8m – and should use this to keep these jobs public.
"The trust has left us with no option but to press ahead with a two-day stoppage on May 23 and 24 at all sites, including sterile services, which could cause disruption.
"Unite’s door is open 24/7 for constructive talks to resolve this dispute."