Unions have warned industrial action could be taken by workers who clean Norwich's streets and keep parks maintained, because of a dispute over pay and conditions.
Some 400 workers, currently employed by Norfolk County Council-owned company Norse are due to transfer to an arms-length company run by the city council, as City Hall takes services back in-house.
The first of the four contracts the city council is taking back, through the newly-formed Norwich City Services Ltd is environmental services, which includes staff who maintain the city's parks and clean the streets.
That contract is due to start next month, but trade unions representing the workers have warned that talks over pay and conditions have stalled.
Representatives from Unite and Unison say City Hall management is "reneging" on commitments to set out a road map to bring the new service's workers' terms and conditions in line with directly employed council staff.
The unions say calls for an industrial action ballot are growing because the company's offer on pay, sickness and holidays "falls well short" of what is required to make progress.
Adam Oakes, Unite regional officer, said: “Despite clear assurances from leaders of the city council about levelling pay and conditions, those commitments are now not being honoured by the board of Norwich City Services Ltd.
"Management failures have caused pay talks to stall and there is a real possibility of an industrial action ballot."
Jonathan Dunning, Norfolk County UNISON branch secretary, said: “Many of our members are on statutory minimum entitlement for annual leave, statutory sick pay and pay rates far below their city council colleagues.
"They have delivered services for Norwich City Council for years and all they want is equality and fairness with their colleagues."
A city council spokesperson said they were "surprised with the unions' stance" and "very disappointed" about the threat of strike action.
She said: “From the beginning of the negotiations, we have fully engaged and worked well with the unions."
She said: "The pay offer for 2021-22 includes a pay increase, more generous sick pay, increased holiday entitlement, and more generous pension entitlements.
“In addition, the council is also investing in a new, modern depot, new vehicles and other benefits which will improve the working environment for staff."
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