Top unionist Tony Church says staff and users will suffer if plans to scale the service down get the green light.
But the Benefits Agency's District Manager, Glyn Pridding, insists the changes won't harm anyone.
At a public meeting at Northwich Memorial Hall last Thursday, Mr Church launched a stinging attack on Mr Pridding and his colleagues.
"They tell us that the benefits office will remain as an 'outlet', with the bulk of the service moving to Chester," he said.
"They may do that, but it will not last. The office has been put on a list of 'flexible properties', which means they are definitely looking to close it.
"Maybe not today, maybe not tomorrow - but you will lose it."
Over 50 people attended the meeting, including members of the Cheshire Deaf Society and staff from Northwich's Citizens' Advice Bureau.
Mr Pridding declined to attend but later told the Guardian that his staff were discussing the future of the building with the people concerned.
He said he refused to attend the meeting because he did not feel that an open argument with the union was the best way to resolve the matter.
"I can confirm firstly that the office won't close, and secondly that every single service which the consumer currently enjoys there will remain," he said.
"What we are talking about is moving the processing side of things to Chester, which means perhaps 50 of the 70 staff."
He added that compensation would be paid to any staff who would have to commute to Chester.
He went on: "If there is a member of staff who cannot feasibly make that move, they can be relocated at the Northwich office."
He explained that the changes have come about because of a buy-out of the agency's larger sites by Trillium, a group of companies which may sell off the land to developers.
Mr Pridding admitted that the current office, which is at Hartford House on Sheath Street, may face closure in the future.
But he said a new home, still in the town centre, would be found if that happened.
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