Media speculation has suggested Brown will be accompanied by transport and industry secretary Alistair Darling to discuss the future of the site.
"It is possible the chancellor would visit the Ellesmere Port factory on Wednesday," said a Treasury spokeswoman. She added that nothing had yet been confirmed.
Unions said they feared tomorrow was now the likely day for the job losses to be announced.
GM announced last week that a third of staff could go at the Merseyside factory in order to meet reviews of production capacity across its three Astra model plants in Europe.
GM will face a backlash from worker’s union Amicus, which said it will terminate its £8 million fleet contract with Vauxhall, if jobs go at Ellesmere Port.
Derek Simpson, Amicus general secretary, said: "Unless General Motors are prepared to treat decent men and women in Britain with some dignity we will cancel our £8m contract for Vauxhall cars.
"We will encourage our members to buy their cars from a manufacturer who supports the British economy and urge other unions to do the same.
"We will be meeting with Japanese manufacturers who employ UK workers and explore options for sourcing our car fleet from them."