U.S. labor board issues a complaint against Starbucks.

The National Labor Relations Board issued a complaint against Starbucks on Tuesday over accusations that it retaliated against two employees seeking to unionize their store in Phoenix.

The workers are part of a campaign that has created unions at six stores in the Buffalo area and Arizona since December, out of roughly 9,000 company-owned stores nationwide. Overall, workers at more than 100 Starbucks locations have filed for union elections during that time.

The formal complaint — something a regional office of the labor board issues after investigating and finding merit in accusations against employers or unions — is the first of the current Starbucks campaign. It contends that Starbucks issued a written warning to one employee and suspended her, and rejected the scheduling preferences of a second employee, leading to her termination, because the employees supported the union.

In addition, the complaint states that the first employee, Laila Dalton, was suspended and disciplined for raising concerns about wages, hours and insufficient staffing on behalf of co-workers, and that the retaliation was intended to discourage other employees from raising similar concerns, even though it is their legal right to do so.

If the regional office is successful in prosecuting the case through an administrative law judge, Starbucks will have to advise employees of their rights to engage in protected activities like complaining about wages and staffing. The company would also have to make the second employee, Alyssa Sanchez, whole for the losses she suffered as a result of her effective termination. The agency could seek other remedies as well. The company could appeal the decision to the full N.L.R.B. in Washington.

“Today is the first step in holding Starbucks accountable for its unacceptable behavior during the unionizing efforts in our store and stores around the country,” Bill Whitmire, a barista at the store who is involved in the union campaign, said in a statement. “Laila and Alyssa were traumatized, and their hope is that no other partner EVER has to go through what they have gone through.”

Reggie Borges, a company spokesman, reiterated previous denials of accusations of anti-union activity.

The union representing Starbucks employees, Workers United, an affiliate of the Service Employees International Union, has brought similar charges on behalf of other workers around the country, including roughly 20 two weeks ago.