The new requirement adds to a list of labor complaints Starbucks workers have levied against the coffee chain.

Starbucks baristas are walking off the job all over the U.S. following a new dress code policy. But Arizona employees say it's about more than that.

Starbucks and the union had temporarily agreed to collective bargaining over dress code changes as part of ongoing negotiations for a new contract. In December, a bargaining session with the company failed to produce better wage gains.