Workers at a number of Starbucks outlets in the United States have gone on strike in a pay dispute in the lead up to Christmas.

On Friday, about 30 people including Starbucks workers staged a protest in front of a shop in Burbank, near Los Angeles, holding placards that read "No Contract, No Coffee."

The Starbucks workers' union representing more than 10,000 employees at more than 500 stores across the US said the strike will continue until Tuesday. It is demanding the company raise wages and resolve unfair labor practice charges.

Workers have also gone on strike at outlets in Chicago and Seattle, where Starbucks is headquartered.

A worker at the Burbank outlet said the strike is escalating each day and that he expects it to spread nationwide on Tuesday.

Meanwhile, drivers delivering merchandise for Amazon also began a strike on Thursday, demanding higher wages. They staged protests at seven delivery hubs in the state of New York and elsewhere in the US on Friday. The drivers are members of a logistics-related union.

The Associated Press quotes an expert as saying the workers are trying to achieve results before President-elect Donald Trump takes office in January. The expert noted that Trump is expected to take a less friendly stance toward unions compared with the current Democratic administration.