"Savage cuts" to Richmond Council's budget could lead to job losses and services being cut, a union has said.
The GMB said the south-west London council was planning to cut £35m from its annual budget of £143m.
GMB official Paul Grafton said the cuts were "a result of the government's Comprehensive Spending Review".
Richmond Council leader Nicholas True said the cuts were needed to "protect vital services" and "postponing or avoiding action is not an option".
Mr Grafton said: "There are savage cuts coming down the line in the London Borough of Richmond as a result of the government's Comprehensive Spending Review.
"We are attempting to establish the level of job losses and cuts to services."
'Difficult years ahead'
The council could also begin sharing services with the private and voluntary sectors, reducing the number of services delivered by the local authority, the union said.
In October Communities Secretary Eric Pickles said other councils should follow the example of Hammersmith and Fulham, Kensington and Chelsea, and Westminster which have agreed to merge some of their services.
The three councils admitted there would be "significant" staff reductions as a result but said they could save up to £100m.
Councillor Nicholas True said: "The economies which Richmond Council will have to make are as a direct result of the financial situation in which the country finds itself.
"If we are to protect vital services for our local community while at the same time ensuring we keep the council on a sound financial footing for the difficult years ahead we absolutely must do this. Postponing or avoiding action is not an option."