A march and rally will be held tomorrow in support of Kinsley Academy cleaners who have been on strike for 30 days.
Supporters of the three women will gather in Barnsley for a protest against C&D Cleaning Services Ltd, the private company which employs them.
Public sector union Unison, which is representing Lesley Leake, Marice Hall and Karen McGee, claims the company cut their pay, holidays and sicknes entitlement after taking over the school cleaning contract.
Barnsley-based C&D Cleaning has so far declined to comment on the claims by Unison and talks have failed to resolve dispute.
Supporters of the strikers include Labour leader Jeremy Corbyn, shadow chancellor John McDonnell, Hemsworth MP Jon Trickett and the comedian Mark Thomas.
Unison regional organiser Robin Symonds said the cleaners had lost hundreds of pounds because of changes to their contracts at the Wakefield Road school.
He said: “The three women have worked at Kinsley Primary School for a total of thirty years but soon after it became an academy their jobs were outsourced and they transferred from Wakefield Council to C&D Cleaning services.
“People don’t like unfairness and there has been a lot of support from all over the country for the women. Jeremy Corbyn and John McDonnell have added their support and comedian Mark Thomas has raised hundreds of pounds for the hardship fund.
“Saturday’s rally will be an opportunity for supporters to send a clear message to their employer to treat them fairly and pay them what they are owed.”
Tomorrow protesters will gather outside Barnsley Town Hall before marching to the town’s Mayday Green for a rally and speaches.
Kinsley Academy is part of Wakefield City Academies Trust, a chain of 20 schools.