The future of 1,000 jobs at Vauxhall's Ellesmere Port plant in Cheshire remain in doubt following talks with parent company General Motors (GM).
The Ellesmere Port factory employs 3,000 people in total
Unions described the talks, which took place in Germany, as "unhelpful".
Reports that Gordon Brown and Trade Secretary Alistair Darling may visit the site on Wednesday also heightened fears for the future of workers there.
When the MG Rover factory closed last year, the Chancellor visited to offer aid packages to the staff.
The Treasury said it was "possible" Mr Brown may visit Ellesmere Port.
As a result, union leaders said they feared Wednesday was now the likely day for the redundancies at the factory to be announced.
Vauxhall reportedly wants to make the redundancies at its Cheshire factory as part of a cutback in the production of its Astra model.
Unions admit that changes need to be made if GM is to stem its losses in the difficult European market, but they have called for any cuts to be spread across the group's European factories.
However, representatives from Amicus and the Transport & General Workers' Union said talks with GM in Germany had been difficult, adding that tough decisions lay ahead.
GM representatives declined to comment as they left the talks late on Monday.
Last week, GM Europe chief Carl-Peter Forster hinted that redundancies across Europe were a less attractive option, as the UK market would be "more capable" of absorbing job cuts.
Ellesmere Port may follow Coventry as the car industry's latest casualty
The threat of 1,000 people, or a third of the workforce, being axed at Ellesmere Port was first revealed last week, sparking a wildcat strike.
It followed GM Europe's announcement that it was reviewing production capacity across its three Astra plants in Europe as it expects demand for the car to decline.
UK Trade and Industry Secretary Alistair Darling said on Monday that the government had been in contact with both sides at Vauxhall.
"The government is being kept fully informed and once we know what General Motors' position is, we can say something further," he said.
Mr Darling added that he held out hope that the Ellesmere Port factory could be chosen by Vauxhall to build a new model in the future.
Workers at the site have expressed their dismay at uncertainty surrounding the plant.
"We feel hard done by, we've done a lot for the plant and they've not given any respect back," one worker told the BBC.
"We don't know what the score is ... We're all pretty down, as can be expected."
Amicus is threatening to take its car fleet deal away from Vauxhall if it cuts jobs at Ellesmere Port.
"Unless GM are prepared to treat decent men and women in Britain with some dignity we will cancel our £8m ($15m) contract for Vauxhall cars," said Amicus General Secretary Derek Simpson.
He said the union would encourage its members and other unions to buy cars from makers that support the UK economy, while adding it was planning to hold talks with Japanese firms making cars in the UK about supplying its fleet.