"It is clearly an emotional reaction to a very difficult situation.
Around 200 workers entered the company's management headquarters on Wednesday morning chanting "Judas", demanding to speak to General Motors' chief executive Nick Reilly.
Mr Reilly, who agreed to come out after workers left the foyer, said that job losses were not just restricted to the UK and that around 5,000 positions would be lost from the company's European plants.
A spokesman for the Amalgamated Engineering and Electrical Union said the workers' reaction was entirely expected.
"It is clearly an emotional reaction to a very difficult situation.
"People have been told they are losing their jobs, told just before Christmas and told over the radio."
The government has promised help for Luton after the announcement that the car plant would close with the loss of about 2,000 jobs.
Trade and Industry Secretary Stephen Byers has described the decision, which may have a severe impact on the local economy, as "a bitter blow" for workers.
Mr Byers said his department would target "rapid response units" to the town, offering advice on retraining and special loans for people who want to set up their own businesses.
Unions have called for tough government measures to prevent similar closures after an extremely difficult year for motor manufacturing in the UK.
Tories blame red tape
There is now a political argument over what caused GM to decide end car production in Luton.
The Conservatives are blaming government bureaucracy but Vauxhall has pointed the finger at low demand for the Vectra model manufactured at the plant.
The company is losing £600m a year in Europe but the high value of the pound against the euro is not thought to be a factor in the decision.
TUC general secretary John Monks said the government could "create a tougher climate for multi-national companies in this country".
"Make it harder for them to exit in the way that General Motors are doing in Luton," he urged.
The Bedfordshire plant had been regarded as one of the most secure in the UK.
About 500 of the workers are expected to be transferred to Vauxhall's neighbouring factory making vans, which is not affected.
Redundancy package
BBC industry correspondent Stephen Evans said General Motors in Detroit decided to close the car plant as it reorganises its worldwide operation.
The company plans to concentrate production of the Vectra's replacement on the continent, primarily in Germany but also in Holland.
The jobs will go over the next 15 months, with workers offered a "very reasonable" redundancy package.
Vauxhall Chairman Nick Reilly said the decision was necessary to retain competitive manufacturing in the UK.
It has been a tough year for motor manufacturing in Britain.
In addition to the end of car production at Ford's factory in Essex in 2002, with the loss of thousands of jobs, loss-making Rover also laid off thousands after it was sold by BMW.
Car firms, facing industry-wide overcapacity in Europe, have been hit by the strength of the pound against the euro when exporting UK-made cars to continental Europe.