Federal labor officials have asked a judge to order Starbucks Corp. to return three union activists to their position in its Phoenix location, alleging that the company committed unfair labor practices, the Associated Press reported.

In a Friday filing in the US District Court in Arizona, the National Labor Relations Board's (NLRB) Phoenix regional director sought an injunction that would make Starbucks reinstate the three employees.

The NLRB's petition is the latest setback for the coffee company, as its employees across the country seek to unionize. Workers at the flagship Seattle location voted to form a union on Thursday, and Colorado baristas did the same on Friday, mentioned AP.

Federal labor officials in Phoenix accused Starbucks of retaliating after it knew that its employees are seeking to unionize.

"Among other things, Starbucks disciplined, suspended, and discharged one employee, constructively discharged another, and placed a third on an unpaid leave of absence after revoking recently granted accommodations," the filing indicated.

A Starbucks spokesperson said on Saturday that the company disagreed with the NLRB allegations and claimed that an investigation showed that the employees violated policies and state law - in some cases.

Following the Seattle location's vote, Reggie Borges, a Starbucks spokesperson, said said "we will respect the process and will bargain in good faith. We hope that the union does the same."

Starbucks threatens employees against unionization

Earlier this year, many employees were inspired by the unionization of Starbucks stores in Buffalo and began discussing organizing their business.

In March, workers at a Starbucks trying to unionize got a letter from store management stating that if they vote to unionize, "benefits and salaries will essentially be frozen" until a bargaining agreement is reached.

VICE News got the letter, which strongly suggests that the firm aims to prolong the collective bargaining process.

“Generally speaking, if the union gets the votes needed to represent you, good-faith negotiations can often take more than a year—if a contract is reached at all,” states the letter, dated March 21 and signed by store managers in Olympia, Washington. “If a union is certified, benefits and wages will essentially be frozen while the parties negotiate the contract.”