A strike by Starbucks workers over the company's new clothing rules got bigger on Thursday.

Starbucks Workers United, a union for the company's U.S. employees, says over 2,000 baristas at 120 stores across the U.S. have been striking since Sunday to show their disapproval of the new dress code.

From Monday, Starbucks is introducing new rules about what staff can wear under their green aprons. Employees in the US and Canada working in Starbucks-owned and licensed stores will need to wear a plain black shirt and trousers or jeans in khaki, black, or blue denim.

Previously, baristas could wear more dark colours and patterned shirts. Starbucks believes the new rules will make its green aprons more noticeable and help customers feel more at home in its stores, creating a friendlier atmosphere.

However, Starbucks Workers United, the union for employees at 570 of Starbucks' 10,000 US stores owned by the company, argued that the dress code should be discussed and agreed upon together.

Paige Summers, a Starbucks supervisor in Hanover, Maryland, believes Starbucks has lost its focus. She argues that instead of valuing the input of baristas who create the Starbucks experience, the company is concentrating on irrelevant issues, such as a strict new dress code. Summers added that customers are unlikely to be concerned about employee uniform colours when faced with long waiting times for their drinks.

Summers and others also pointed out that Starbucks was selling clothing with its brand on an internal website, even though employees weren't allowed to wear those styles at work anymore. Starbucks had said they would give each employee two free black T-shirts when they announced the new dress code.

On Wednesday, the Starbucks Workers Union announced that 1,000 employees had participated in walkouts across 75 stores in the US. Starbucks responded that the strikes had a minimal effect on its 10,000 company-run stores in the US, with some stores only closing for short periods.

"Starbucks stated that it would be better if the union focused on returning to negotiations with as much energy as they are using to protest by wearing black shirts. They added that over 99% of their stores are currently open and serving customers, as they have been throughout the week."

Readers of the Associated Press expressed varied opinions on the dress code, with some arguing that Starbucks baristas' concerns were overstated, as many retailers have similar requirements. Others felt Starbucks should prioritise beverage quality, pricing, and employee satisfaction over strict dress codes.

Maddie Mucklow, a Starbucks store manager in Seattle, has expressed her support for the proposed regulations.

Mucklow admitted that the new dress code presented some challenges for her store's employees. However, she believes it creates clearer expectations for professional appearance while still allowing for personal expression.

Since 2021, Starbucks Workers United has been organising unions in Starbucks stores across the U.S. Despite agreeing to negotiate again in February 2024, Starbucks and the union have not yet reached a final agreement.

This week, the union announced they had officially complained to the National Labor Relations Board, claiming Starbucks was not negotiating the new dress code.