Democratic presidential candidate Barack Obama has written to Tesco CEO Sir Terry Leahy to urge the retailer to recognise workers unions in the US.

The letter follows claims from US union The United Food and Commercial Workers' Union that Tesco had failed to recognise it and called for the same rights for workers at Tesco's US venture Fresh & Easy Neighborhood Market as its UK workers.

“I am aware of Tesco's reputation in Britain as a partner to unions,” Obama wrote. “I would hope that you would bring those values to your work in America.

“It is in your interest to ensure that the communities where you do business and the leaders of workers in the industry are heard and that their concerns are heard and respected,” he added.

Tesco denied it had failed to recognise the union. “Our position has been clear for some time,” a spokesman told the Guardian. “If Fresh & Easy staff want to join the union they can.”