OVER 300 caretakers and cleaning staff in 20 schools across Kirklees could go on strike.
They work for schools run by the Jarvis company and are unhappy with their pay and conditions.
The workers in these schools are no longer employed by Kirklees Council, but by Jarvis.
Union chiefs say their pay and conditions are not as good as for their council counterparts - despite doing the same job.
Fears have also been expressed that this will lead to an exodus of cleaning staff from these schools.
Mike Foster, joint chief education steward for Kirklees Unison, said: "We have met all the Jarvis staff and they have voted unanimously to take industrial action if their wages and conditions don't go back to council wages and conditions."
The action will involve about 340 caretakers and cleaning staff across the Kirklees area.
Mr Foster said Jarvis had not renewed any of the cleaning equipment.
He added: "Our members have not benefited from the equal pay settlement that cleaners across Kirklees got, because both the council and Jarvis refuse to acknowledge the claim.
"Next April cleaners' pay in Kirklees 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.
"I think the major problem for the schools is that they don't employ the cleaners and therefore they can't deploy the cleaners as they wish."
Mr Foster said that if this situation continued there could be huge problems.
"At Colne Valley High School they were eight cleaners down last year.
"Jarvis is a company that people don't want to work for. If they're going to get better pay and conditions working for the council, then why work for Jarvis?
"The Jarvis cleaners, who used to work for Kirklees, feel like second-rate citizens, despite working their socks off to try and maintain standards.
"They're angry that a recent report found that standards had slipped."
He also said the Jarvis cleaners had had four employers in four years.
Asked about the PFI arrangement with the schools Mr 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."
Union officials are due to meet Kirklees next week.