Unite’s Len McCluskey said there are “no assurances” offered to Vauxhall workers after meeting with UK business secretary Greg Clark and General Motors president Dan Ammann on Thursday.
Peugeot and Citroën owner PSA Group is in talks with General Motors to buy its loss-making European Opel brand, which owns Vauxhall in the UK and includes British plants at Ellesmere Port and Luton.
Mr Ammann, who flew to Germany on Wednesday to meet government officials concerned about the deal, met Mr Clark on Thursday and then had a separate meeting that included both men and union leader Mr McCluskey.
“There’s no assurances at the moment,” said Mr McCluskey, after the meeting, though he added that “concrete proposals are imminent” from the companies.
These are expected within the next two weeks, when Mr McCluskey is due to meet Unite shop stewards at Vauxhall.
He added: “This is an unfolding story and we wait to hear what the next installment is.”
Mr Clark, who had a separate meeting with Mr Ammann before Mr McCluskey joined, called the talks “constructive”.
He said: “There is some way to go in discussions between GM and PSA but I was reassured by GM’s intention, communicated to me, to build on the success of these operations rather than rationalise them.”
However, he did not say whether the US carmaker had offered assurances over jobs.
German and French ministers are meeting over concerns about job losses that may result from the deal.
Peugeot chief executive Carlos Tavares is expected to slash costs in the business to restore it to financial health.
Mr McCluskey said there was a danger that a deal would be struck between the German and French governments over the future shape of the company without Britain at the table.
He said the government should make sure that Britain is “not sitting on the sidelines” with the companies “playing one worker off against another”.
Neither the UK government nor Unite have been able to secure a meeting with PSA since the talks were publicly announced on Tuesday.
Mr McCluskey said he is “seeking a pretty urgent meeting” with Mr Tavares, adding: “I’m sure we’ll get a positive response.”
In a statement after the meeting, GM said: “While we have no definitive news to report at this time, we can affirm that our objective in exploring opportunities with PSA is to build on the success of Opel-Vauxhall and to put the business and the operations in the strongest possible position for the future.
“We look forward to engaging with our stakeholders as part of these ongoing discussions.”