America's biggest food workers' union has stepped up its pressure on Tesco's US operation, by reporting its ready-meals supplier in the US to a labour-relations tribunal yesterday for the alleged unfair firing of six employees.

The United Food and Commercial Workers Union (UFCW) claimed that the 2 Sisters Food Group, a supplier to Tesco's Fresh & Easy convenience store chain, has sacked the workers for their attendance at a union recruitment meeting and for filing complaints against managers.

This is the latest broadside the UFCW has launched against Fresh & Easy's failure to recognise the union in the US, following their attendance at the grocer's AGM in Birmingham in June and two letters from Democratic presidential nominee Barack Obama to Fresh & Easy boss Tim Mason and Tesco chief executive Sir Terry Leahy.

UFCW campaigns director Emily Stewart said: "We have uncovered evidence that workers are being harassed and intimidated by 2 Sisters management to deter union activity, in clear contravention of US labour laws."

2 Sisters stressed that it is "very committed" to its $60m investment into its food-processing facility close to Fresh & Easy's distribution centre in Riverside, California, where it aims to create 400 local jobs over the next four years.