Starbucks (SBUX) is imposing new limits on what its baristas can wear under their green aprons.

Starting May 12, employees will be required to wear a solid black shirt and khaki, black or blue denim bottoms. Shirts can be short- or long-sleeved and collared or collarless, the company said in a memo released Monday. Starbucks will give each employee two free T-shirts.

Starbucks said the new dress code will make its green aprons stand out and create a sense of familiarity for customers. It comes as the company is trying to reestablish a warmer, more welcoming experience in its store.

“By updating our dress code, we can deliver a more consistent coffeehouse experience that will also bring simpler and clearer guidance to our partners, which means they can focus on what matters most, crafting great beverages and fostering connections with customers,” the company said in a post on its website.

But some workers protested the move. Starbucks Workers United, a labor group that has unionized workers at more than 550 of Starbucks' 10,000 company-owned U.S. stores, said it told the company last week that it has already negotiated a tentative dress code agreement during bargaining sessions with the company. The union said it opposes any changes to the dress code until bargaining concludes and a labor agreement is reached.

Jasmine Leli, a Starbucks barista and union bargaining delegate, said the company should be focusing on things that improve store operations, like appropriately staffing stores and giving workers a guaranteed number of hours.

“Instead of addressing the most pressing issues baristas have been raising for years, Starbucks is prioritizing a limiting dress code that won’t improve the company’s operation," Leli said in a statement provided by the union. “They’re forcing baristas to pay for new clothes when we’re struggling as it is on Starbucks wages and without guaranteed hours.”

The new guidance comes nearly a decade after Starbucks loosened its dress code to give employees more opportunity for self-expression. In 2016, the company expanded the color of shirts employees could wear, adding gray, navy, dark denim and brown to the previous guidance of black or white. It also allowed patterned shirts in those colors.

In 2019, the company tweaked the dress code again, allowing one facial piercing as long as it was no larger than a dime. The new dress code still allows one facial piercing.