Pressure group Searchlight told Marketing Week it is urging its supporters to write to advertisers such as brewer Molson Coors and Tesco to ask them to add their weight to its campaign.
Searchlight is escalating its campaign after Clear Channel refused to end its deal to carry the BNP’s controversial European election campaign posters.
Searchlight says almost 7,000 letters were sent to the company by its supporters over the past couple of weeks.
The group is targeting the media owner for profiting from “racist propaganda” by selling poster sites to the far right party.
The billboard company’s clients will now come under pressure from campaigners to take a stand on the issue.
However, a Clear Channel spokeswoman says it has responded to each letter sent quoting its policy on political party advertising.
The policy says the laws governing political advertising “allow legal and legitimate political parties to engage in campaigning and maintain free speech”, and that it will accept advertising from such parties without “bias or favour, regardless of the company’s own views”.
The response continues that it is not for Clear Channel to “censor” such messages if they are legal, or “bow to pressure from lobby groups and activists”.