Unions are using "stone age economics" by asking customers to boycott Peugeot cars, the head of the Confederation of British Industries (CBI) has said.
Adverts and posters have run in national papers
Richard Lambert, CBI director-general, made the comments following a protest by union members outside the British Motor Show in London's Docklands.
Unions began the campaign after Peugeot said it planned to close its plant near Coventry with the loss of 2,300 jobs.
Mr Lambert also criticised calls for stronger labour laws in the UK.
The Amicus and Transport and General Workers' Unions have funded a £1m advertising campaign in the national media to persuade people not to buy Peugeot cars.
Staff have picketed Peugeot dealerships nationwide and urged customers to buy cars which are built in the UK.
But Mr Lambert said the idea that goods sold in the UK should be built in the UK was "stone age economics".
He said unions should consider the effect of stricter employment laws in other European countries because many had much higher unemployment rates than the UK.
Peugeot is one of the exhibitors at the Motor Show which opened to the media on Tuesday. It is the first time in 30 years the event is not being held in Birmingham.