Union leaders have been forced to withdraw a radio advert asking car buyers to boycott Peugeot over the closure of the Ryton plant in Coventry.
Adverts and posters have run in national papers
The advert breached advertising standard codes barring unions from making political adverts and will not be aired.
They said their campaign is being gagged and want the law to be changed.
The ad featured the voices of well-known actors encouraging listeners to "Think of England".
Day of action
The radio advert continued the £1m campaign run by the Transport and General Workers Union (T&GWU) asking buyers to boycott Peugeot in support of the 2,300 workers who will be made redundant with the closure of Ryton.
The campaign included adverts and posters in national newspapers.
The item featured the familiar voices of actors from the BBC soap EastEnders and ITV's Coronation Street and Where the Heart Is.
But it broke section 15 of the Radio Advertising Standards code which limits trade unions to advertising their services to members and prevents them from making political adverts.
Day of action
The advert was going to run four times a day on independent radio stations during August.
T&GWU general secretary Tony Woodley said: "The public need to know we are fighting back with our members in Peugeot against the closure of a profitable car plant.
"And they need to know there is support from industry experts and show business for our campaign.
"The law has gagged us from saying this on the radio, but we'll say it all the same."
The union is planning a national day of action this Saturday where demonstrations will take place at Peugeot dealerships across the UK.