The NSW government is accused of trying to privatise Sydney's public transport "via stealth", as it flags redundancies for bus and train cleaning staff.
The Rail, Tram and Bus Union (RTBU) says that after three years of "restructures", Sydney's train cleaners have had enough, and more than 60 per cent of staff have applied for redundancies.
It says 437 of 713 staff have expressed interest in taking a redundancy, as the government plans to outsource about 35 per cent of its cleaning of the network.
RTBU State Secretary Alex Claassens said the outsourcing had stoked concerns the government was "silo-ing divisions of the network, gutting them and then moving to privatise them".
"Workers and the union have long suspected the government's privatisation plans, but outsourcing jobs within the cleaning division is the first public move to privatise jobs and sell off the network," he said in a statement on Monday.
The RTBU said the government sent out expressions of interest for redundancies or redeployment in December to more than 100 cleaners working on Sydney's buses.
However, the union's acting state secretary, David Woollams, said he did not believe the take-up of redundancies would be as high by bus employees as those on trains.
"The buses haven't gone through major restructures like the rail has," he told AAP on Monday.
Minister for Transport Gladys Berejiklian has defended the move on Sydney's trains, saying that "having the same staff doing the same old thing is not working".
"Anyone who thinks trains are as clean as they can be is kidding themselves," she said in a statement.
She said the push to outsource one-third of the workforce would drive innovation and improved service.
"Successful tenders will have to meet market-leading standards of cleaning, so our customers will notice even more improvement."
Sydney Trains said work practices meant a number of senior cleaning staff spent more time filling out reports than cleaning trains and stations.
In a position statement, Sydney Trains claimed it was time to review practices to give customers cleaner trains and taxpayers better value.
Tenders for cleaning functions are expected to be released to the market in coming months.
New arrangements are expected to be implemented by September 2014.