Some 340 caretakers and cleaning staff in 20 schools across Kirklees, West Yorkshire, may strike.
The workers in these schools are no longer employed by Kirklees council, but by the company Jarvis.
They are unhappy with their pay and conditions which the Unison union says are not as good as for their council counterparts - despite them doing the same job.
Mike Foster, joint chief education steward for Kirklees Unison, said, “The Jarvis staff have voted unanimously to take industrial action if their wages and conditions don’t go back to matching council wages and conditions.”
He added, “Next April cleaners’ pay in Kirklees council is set to go up in line with equal pay legislation. But Jarvis cleaners won’t get that because they don’t work for the council.
“The Jarvis cleaners, who used to work for Kirklees, feel like second rate citizens, despite working their socks off to try and maintain standards.”
He also said the Jarvis cleaners had worked for four employers in four years.
Asked about the Private Finance Initiative (PFI) arrangement with the schools, Mike Foster said, “It’s been an absolute fiasco that has become a tragedy for the schools, the pupils and the staff and, because of that, for parents as well.”