Starbucks is accused by the union of avoiding paying the Living Wage – which is set at £8.55 in London and £7.45 outside. The company claims pay is just one of a range of benefits its 'partners' (staff) receive.
The Living Wage is a voluntary rate, but considered the minimum to give workers a basic standard of living.
The GMB's national equality officer, Kamaljeet Jandu, said: "As well as not paying its fair share of tax, Starbucks is avoiding paying a living wage of £8.55 an hour in London and £7.45 elsewhere."
Jandu added: "Starbucks is a million miles away from empowering its staff and helping them exercise their rights to join a trade union and have it recognised. GMB members in the company are afraid they will be victimised if managers knew they are members of this union.
"It really is an anti-social company."
Starbucks, which is in talks over tax, said staff were consulted about the new conditions and pay was just one of a range of benefits.
A spokeswoman for Starbucks said: "The decisions we have taken over the past few months have been about finding the right way to structure packages so that they are balanced across pay, benefits and development.
"Pay is one of a range of benefits that partners receive at Starbucks."
