The coordinated global action is unlikely to directly affect the company financially. It comes as the US union tries to ramp up pressure on the chain after negotiations stalled.
In the UK, rallies organised by the union Unite are set to take place in London, Norwich and Glasgow, the union said. Workers in Glasgow will join a work stoppage.
Coordinated demonstrations are also planned at Starbucks stores and offices in cities across Australia, Brazil, Canada, Italy, the Netherlands, Germany, Switzerland and Turkey. Also on Wednesday, baristas are gearing up to protest at the largest Starbucks in the world, in Chicago.
"Starbucks executives need to know: wherever Starbucks is, our picket lines will be there too," Diego Franco, a barista from Chicago, said in a statement.
The company maintains that its pay and benefits are industry-leading, and that baristas continue to get more hours of work per week on average.
Starbucks has in recent years faced consumer boycotts, a wave of new competitors and a customer backlash over high prices, as well as turmoil in its leadership ranks.
The chain, under chief executive Brian Niccol, has been working to bring back customers, promising faster service and a return to its coffeehouse roots, with ceramic mugs and hand-written notes.
It has also outlined plans to invest more than $500m to improve staffing and training.
In October, Starbucks reported 1% growth in sales at global stores open at least one year - its first quarterly increase in almost two years. But in the US, sales were flat.