Hundreds of NHS workers currently out on strike are believed to be preparing to head to the picket line again if their employment dispute is not resolved.
Unions supporting the protests against the creation of subsidiary firm WWL Solutions have promised to continue with industrial action until the campaign is won.
Estates and facilities employees, including porters, domestics, caterers and switchboard operators, have downed tools today (Wednesday) and tomorrow.
At the lunchtime rally in Believe Square in Wigan town centre there was deep anger about the move by bosses at Wrightington, Wigan and Leigh (WWL) NHS Foundation Trust, with many speakers saying the wholly-owned firm represents privatisation by the backdoor.
Wigan MP Lisa Nandy travelled up from London to be presented and pledged her full backing for as long as the dispute lasts.
Ms Nandy said: "This proposal is bad for staff, bad for patients and bad for Wigan. It's bad for our NHS. It attacks the pay and pensions and collective bargaining that underpins the way our NHS has been run through the last 70 years.
"It's deliberate, don't let anyone tell you otherwise. The NHS has been under-funded to force trusts into making proposals like this to line the pockets of private companies.
"Every time I go into Wigan Infirmary I see staff working longer hours, staying after their shifts, going the extra mile for patients because they believe in our national health service. This is our most precious asset.
"I've never been as proud to be your MP as I am today seeing the show of solidarity and strength. Wigan is grateful for what you are doing. I will stand with you on the picket line and fight this battle for as long as it takes."
The Wigan strike is thought to be the first full-blown walk-out over the introduction of subsidiary companies in the country.
This afternoon the issue will be put centre stage in Parliament with a House of Commons debate introduced and led by Labour's shadow secretary of state for health Jon Ashworth.
The Believe Square rally was addressed by union representatives, councillors and workers, with messages of support being received from organisations across the country.
One of the most fiery and passionate addresses came from Wigan Infirmary domestics supervisor Dave Macnamara.
He said: "This proposal is unjust and unfair and we are all showing we will not take it. This is our NHS, not theirs.
"WWL Solutions is nothing but greed. It is Tory Government policy to disassemble the health service and sell it off to the greedy few.
"The public needs our hospitals to be in the best condition they can be, as they were intended to be right from the start. This is our time to resist and win."
Coun George Davies, who worked for 36 years as a Wigan Infirmary porter, described the WWL Solutions plan as "disgusting" while numerous speakers raised the possibility of firms such as Carillion, Serco and Virgin Care being able to get hold of greater chunks of the health service in the future if the proposal was allowed to go ahead.