One of Americas biggest trade unions is calling on Barack Obama to endorse a new campaign condemning Tesco for the way it treats its workforce in the US.

The United Food & Commercial Workers Union (UFCW) said it had little choice but to seek the support of the Presidential candidate after trying in vain to force a meeting with Tesco over the past two years.

It is furious that Tesco refuses to recognise the union at Fresh & Easy, the supermarket giants fledging business in California and Arizona.

Emily Stewart, UFCW campaign director, said the union only wanted the same constructive relationship that Tesco has with Usdaw, the shop workers' union, in the UK.

She said that, unlike staff employed by Tesco in the UK, workers at Fresh & Easy have no written contract. She added that many were ineligible for health care insurance and also have to count sick leave as holiday.

We are not here to make mischief, she said. We are here to make a stand for basic employment rights. Tescos reputation is being sullied by its behaviour in the US.

Mr Obama wrote to Tim Mason, Fresh & Easy's chief executive, in November, urging him to engage with community organisations in Los Angeles and to begin talks about union recognition.

Ms Stewart said: We are absolutely continuing a dialogue with Mr Obama, and we feel he supports what we are trying to do.

Jon Cruddas, the Labour MP who stood for the deputy leadership of the party last year, said Tescos stance was undermining the reputation of British companies around the world.

Speaking at the launch of the UFCWs Two Faces of Tesco campaign today, Mr Cruddas said he would be urging Sir Terry Leahy, Tesco chief executive, to meet the union.

He said: What this dossier exposes about Tescos practices in the United States in my view not only undermines Tescos reputation, but will also affect how people think about the fairness of British companies in general.

A Tesco spokeswoman was not immediately available for comment.

The supermarket today announced that its 193,000 staff in the UK would be sharing almost £92 million in the latest payout under its share-save scheme.