Tesco has refuted claims from an international trade union which criticised the grocer’s employment practices in some of its overseas markets.

The UNI Tesco Global Union Alliance criticised Tesco’s practices in Thailand, South Korea and the US.

It alleged that Tesco “forced” employees in South Korea to work up to 20 hours a week of unpaid “voluntary” overtime and employed contract workers on lower pay. In Thailand, it said the grocer required employees to work two shifts of 18 hours back to back.

A Tesco spokesman said it is a “politically motivated report paid for by a union which is trying to recruit more members”.

He added: “The reports are a travesty and misrepresent the truth. Uni are using a standard tack of going to far off places, producing reports which are very difficult for people in the UK to check. We do check these matters and can tell you that the allegations are untrue.

“We have a strong track record of investing in our people and are committed to making Tesco a great place to work. Wherever we operate in the world, all staff are free to join trade unions and can voice their opinions in a number of ways, including our anonymous annual staff survey. We have productive relationships with unions in a number of countries including Usdaw in the UK and Solidarity in Poland.”