Starbucks has fired a number of workers leading efforts to organise a union in Tennessee, one of more than 50 such drives it is facing across the US.

The coffee chain said the staff had knowingly violated company rules, including by using a store after-hours.

Labour organisers said the firm was retaliating in a bid to slow the momentum of their efforts.

Buffalo, New York recently became home to the first unionised Starbucks-owned stores in the US since the 1980s.