Arou Akot is among 7000 school cleaners who will need to reapply for their jobs for the first time in 24 years.
The NSW department of Finance Services and Innovation has notified United Voice, the union representing the cleaners, that employment guarantees in place since 1994 "will not be extended in the new contracts from 2018".
Mr Akot, a South Sudanese migrant and single father of seven children aged five to 19, has worked for eight years as a cleaner at three schools in western Sydney.
He fears he is at risk of becoming homeless if he loses his job.
Mr Akot said he earns about $1500 a fortnight in the hand and pays $1020 a fortnight in rent.
His work day is split across two shifts from 4.30am to 9am and 2pm to 6pm and he said he was often too busy to take a 10-minute break.
"It is very hard," he said. "We need a job guarantee. If I don't have a job, I will be homeless."
United Voice NSW secretary Mel Gatfield said 7000 NSW school cleaners faced an uncertain future under changes to state government cleaning services.
"For the first time in 24 years, every cleaner will have to reapply for their job, with many facing an anxious wait to see if they will have a job come July next year," she said.
"After years - and in some cases, decades - of service to their school, many cleaners fear that finding another job will be next to impossible, particularly in regional areas."
The union is concerned about the proposed change from an hours-based to a square-metre-based pricing model under the proposed new contract arrangements.
Ms Gatfield said the quality of cleaning was directly connected to having trained staff and enough cleaning hours to do a good job.
"A reduction in staff or cleaning hours will directly impact the quality of cleaning being delivered," she said.
In a letter to the union, Finance Services and Innovation secretary Martin Hoffman said the employment conditions and rates of pay of cleaners would be protected under relevant industrial awards.
He said the same government buildings would need to be cleaned to the same standard under the new contract.
"[So] there will be significant employment opportunities for cleaners," Mr Hoffman said.
"I also understand that under the new contract, all existing cleaners will be offered the chance to attend an interview with the successful tenderers as a way of maximising the employment opportunities for the incumbent workforce."
Alison Redman, a cleaner of seven years, who works at two schools in western Sydney from 6am to 7.30am and 1.40pm to 6pm, is concerned older cleaners will not be rehired.
"I am one of the youngest cleaners and I am 41," she said. "People are not going to want to employ older people, they are going to want to employ younger people.
"It will be difficult finding another job when you have been in the cleaning industry for a long time as most cleaners have.
"Our anxiety and stress levels are through the roof," she said. "Some people are taking mental health days to recompose themselves."
Ms Redman said it would also be difficult for cleaners to work to current standards if their hours were cut.
"That would put so much more pressure on us to get things done. We are struggling as it is," she said.
A spokesman for Finance, Services and Property Minister Victor Dominello said the minister recently met with United Voice. The government would continue to work with stakeholder groups including the union to ensure "existing employees are provided with adequate information regarding the new facilities management contract".
NSW government agencies spend more than $400 million a year on cleaning and maintenance services under the contract, which expires at the end of June next year. The government has said it has a responsibility to ensure the contract delivers the best possible value for money for taxpayers and its agencies.