(Reuters) - Starbucks ( SBUX ) workers have expanded their strike to four more U.S. cities, including New York, the union representing over 10,000 baristas said late on Saturday.

The five-day strike, which began on Friday and initially closed Starbucks ( SBUX ) cafes in Los Angeles, Chicago and Seattle, has added New Jersey, New York, Philadelphia and St. Louis, Workers United said in a statement. It did not say where the New Jersey walkout was occurring.

Starbucks ( SBUX ) did not immediately respond to a request for comment outside regular business hours.

Talks between the coffee chain and the union hit an impasse with unresolved issues over wages, staffing and schedules, leading to the strike.

The union is striking in 10 cities, also including Columbus, Denver and Pittsburgh, during the busy holiday season that may impact the company's Christmas sales.

Workers United warned on Friday that the strike could reach "hundreds of stores" by Tuesday, Christmas Eve.

Starbucks ( SBUX ) began negotiations with the union in April. It said this month it had conducted more than eight bargaining sessions, during which 30 agreements had been reached.

The company operates more than 11,000 stores in the United States, employing about 200,000 workers.