An online storm has broken out over the alleged activities of a vice president of Burger King who is accused of posting anti-activist messages using his daughter's internet identity.

Burger King is currently under pressure from the Coalition of Immokalee Workers (CIW) which has collected around 80,000 signatures on a petition to get the company to pay 1p extra per pound for its tomatoes.

McDonald's and Yum (which owns Taco Bell) have already signed up to the system, which can increase a farm labourer's wages from $50 to $70 per day.

However, an investigation by the Fort Myers News-Press claims that Stephen Grover, vice president of ethical operations at Burger King, has been posting negative comments about the CIW on social networking sites using an identity set up by his daughter.

Fort Myers News-Press highlighted one posting, from 'surfxaholic36', which it believes is representative.

"The CIW is an attack organisation lining the leaders' pockets. They make up issues and collect money from dupes that believe their story," the posting says.

"To [sic] bad the people protesting don't have a clue regarding the facts. A bunch of fools!"

When a Fort Myers News-Press reporter checked at Grover's home, his daughter admitted that she had set up the identity but that the postings were the work of her father.

"I don't really know much about the coalition and Burger King stuff," she said. "That was my dad. My dad used to go online with that name and write about them."

Campaign groups often try to get members to email similar messages to newspapers, a process known as 'astroturfing', but it is highly unusual for an executive to take such an active personal role.

CIW member Gerardo Reyes said: "This is truly disturbing. It's one thing to imagine some kind of anonymous internet stalker out there obsessively tracking every story about the CIW, posting these vicious lies about us and calling us things like 'the lowest form of life' and 'blood suckers'.

"When you realise the person posting those things is actually Burger King's vice president in charge of the ethical operation of the company's supply chain, it really makes you wonder just how high up this whole thing goes.

"Does Burger King, as a company, approve of this sort of behaviour? If not, we'd expect to see some changes now that this has come to light."

Burger King has claimed that Grover's comments are not on behalf of the company, and that it actively investigates how to improve the lot of its workers in the field.

"Comments attributed to Steve Grover do not reflect Burger King's desire to find a way to [ensure] decent wages and modern working conditions for the tomato harvesters in Immokalee," said Burger King spokeswoman Denise Wilson.

"We have a robust vendor code of conduct which mandates zero tolerance for worker exploitation and abuse, and we are open to any responsible suggestions for improvement."