Four years after workers at a Starbucks store in upstate New York became the first to unionize, hundreds of outlets followed – defying intense resistance from the coffee chain. What happened next?

Thousands of Starbucks baristas are on strike across the US, warning the world’s largest coffee chain to brace for the “longest and biggest” bout of industrial action in its history.

Barely a year after Brian Niccol, the Starbucks CEO, tried to draw a line under bitter divisions between its management and unionized workers, pledging to “engage constructively” with them, the American coffee giant is now grappling with an escalating strike during its lucrative holiday trading season.