A convoy of Vauxhall cars driven by the company's workers has driven around Westminster in London as part of a campaign to safeguard their jobs.
The union Unite said it wanted to remind MPs about the uncertain future for the firm's factories in Ellesmere Port in Cheshire and Luton.
Negotiations continue over the sale of GM Europe's European arm Opel, which includes Vauxhall UK.
Potential buyer RHJ International said it would retain the group's UK plants.
Employs 5,000
The Brussels-based outfit is now one of three potential buyers alongside preferred bidder Magna International, the Canadian car parts group, and Beijing Automotive Industry Holding, another late entrant.
Vauxhall employs 5,000 people in the UK, with the Astra model made at its Ellesmere Port site and Vivaro commercial van made at its Luton plant, which is a joint venture with Renault.
A cloud of uncertainty has hung over the UK business after its US parent General Motors filed for bankruptcy protection earlier this summer, forcing it to break itself up and put the European arm up for sale.
"Vauxhall is at the heart of our car manufacturing in this country - an industry, entire workplaces and whole communities need it to thrive"
Len McCluskey, Unite's assistant general secretary, said it was vital that MPs understood that the future of both plants still hung "very much" in the balance.
He added: "These workers are coming to Parliament today because they want MPs to show support for their fight not just for their future, but for the entire UK car industry.
"Vauxhall is at the heart of our car manufacturing in this country. An industry, entire workplaces and whole communities need it to thrive.
"It is vital that any deal done over the future of GM in Europe is the right deal for a secure and lasting industry in this country, which is why we are pressing for our government to carry on doing what it says it is doing and keep working towards a deal which protects our plants and jobs."
Vehicles in the convoy included a 2009 black Vauxhall Vivaro, a silver Vauxhall Vivaro mini bus, a red five-door Astra, the Heritage centre van, a 1966 Viva, 1970 Viscount, 1980 Cavalier, 1982 Chevette and 2002 Vectra.
All were emblazoned with a Save Vauxhall logo.
RELATED INTERNET LINKS
GM
GM Europe
Magna International
Vauxhall History - BBC Feature
The BBC is not responsible for the content of external internet sites
^ Back to top | BBC Sport Home | BBC Homepage | Contact us | Help | ©