Democratic presidential hopeful Barack Obama has written to Tesco’s chief executive Terry Leahy, calling on the grocer to recognise trade unions in the US.

The United Food and Commercial Workers union (UFCW) has won the backing of Mr Obama in its campaign against Tesco, which the union claims treats employees differently at its US Fresh & Easy chain than in the UK.

In a letter to Mr Leahy, Democratic presidential candidate Mr Obama urges the Tesco boss to step in and resolve the dispute.

The Times newspaper, which claims to have seen the letter, quotes Mr Obama as saying: “It is in your interest to ensure that the communities and the leaders of workers in the industry are heard and that their concerns are heard.

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

It is the second letter Mr Obama has written on behalf of the union, which wants to see its members recognised at the stores, as well as better pay and conditions.

In November, Mr Obama wrote to Tim Mason, Fresh & Easy’s chief executive, asking Tesco to work with Los Angeles’ Alliance for Healthy and Responsible Grocery Stores, of which the UFCW is one of the largest members.

The UFCW says it has been seeking talks with Tesco for two years, but the retailer has refused to meet.

UFCW’s campaigns director, Emily Stewart, said: “Tesco has a great reputation for employment rights and corporate responsibility in the UK, but this is a reputation which, in our view, is sullied by its behaviour in the USA.”