Some Starbucks workers in the chain’s largest union are objecting to the company’s new dress code for baristas.

Starbucks Workers United said in a post on Tuesday that baristas around the US are protesting the chain’s implementation of a standard dress code this week.

The union told Business Insider that walkouts had occurred at more than 50 stores as of Tuesday in states such as Wisconsin, Florida, and Pennsylvania.

The union’s website says it represents more than 11,000 workers and more than 570 stores nationwide. As of March 30, Starbucks had more than 17,000 stores in the US.

In a statement to BI, a Starbucks representative said, “Thousands of Starbucks partners (employees) came to work today ready to serve their customers and communities. The biggest update to our dress code is simple: wear a black shirt — either your own or one we provide.”

“Workers United represents less than 5% of our workforce and by their own measure less than 1% of stores have participated in their attempts to cause disruption,” the representative added.

On April 14, Starbucks announced a standard dress code that all baristas must adhere to — a solid-color black shirt, paired with bottoms that are black, blue denim, or khaki.

The dress code, which went into effect on Monday, is meant to “allow our iconic green apron to shine and create a sense of familiarity for our customers,” the company wrote in the announcement.

Starbucks would provide each barista two free shirts as part of the change, it said.

But three baristas BI spoke with said two shirts were not enough for those who work multiple shifts in a week, so they would have to buy clothing.

The workers’ union also said Starbucks should focus on correcting operational problems like understaffing rather than enforcing a dress code.

Starbucks used to have a strict black and white dress code, which it relaxed in 2016 when it allowed baristas to wear shirts of different colors, paired with dark-wash jeans.

The new dress code comes as Starbucks struggles to pull itself out of the red, reporting five consecutive quarters of revenue declines.

CEO Brian Niccol has set up a game plan, which he dubbed “Back to Starbucks,” to boost sales, attract customers to the cafés, and fix problems like long wait times.

This includes implementing a new mobile ordering system, slimming down the menu, and personalizing coffee cups with handwritten memos from baristas.

May 14, 11:05 p.m. — This story was updated to include comments from Starbucks and Starbucks Workers United.