Hundreds of hospital workers including porters, cleaners and catering staff, are to go on strike in a dispute over pay.
The union warned that further strike action will follow if the demands of the workers are not met.
Unite claimed that the mainly black, Asian and ethnic minority staff are paid up to 15% less than directly employed NHS workers.
It's time to end the injustice of a two-tier workforce
Unite general secretary Sharon Graham
Serco said it had recently increased its pay offer to a total of 3%, backdated to last April, adding it was the same as that being received by people directly employed by the NHS.
Unite general secretary Sharon Graham said: “These workers face the same risks as NHS-employed staff but they are paid significantly worse and treated disgracefully.
“Barts Health NHS Trust have a golden opportunity to bring these workers back into NHS employment.
“It’s time to end the injustice of a two-tier workforce. Unite is 100% behind our members’ battle against low pay and exploitation.”
Unite regional officer Tabusam Ahmed added: “Unite gave Serco and Barts over a month to consider their positions before the union announced strike dates. Instead of using that time wisely, they’ve dragged their feet and offered too little too late.
“Barts and Serco must now deliver a pay increase that addresses the poverty pay and the gross inequality of treatment compared to directly employed NHS staff in other hospitals in London.”
Shane DeGaris, deputy group chief executive at Barts Health NHS Trust said: “Over the next 13 months we will be considering future arrangements of the facilities management contract, which could include bringing some services back in-house.
“We are hopeful that this matter can be resolved but are working with Serco to put the appropriate measures in place and ensure hospital services are supported if strike action does go ahead.”
Taddy McAuley, Serco’s contract director for Barts Health, said: “We are extremely disappointed with the notification of strike action from Unite as we recently increased the pay offer for our employees to a total of 3%, backdated to April 2021.
“This is the same percentage increase as that being received by people directly employed by the NHS.
“Serco also recently announced a £100 ex-gratia payment for all of our 52,000 front line employees around the world, including all our colleagues at Barts Health.
“We look forward to further discussions with Unite and hope to work together to find a resolution that avoids the need for this unnecessary strike action.”