The Starbucks Corporation's (SBUX  ) has reached a fevered peak as the National Labor Relations Board (NLRB) takes the company to Federal Court. According to the regulator's Friday filings, the NLRB is petitioning for three former employees fired in retaliation for union organizing to be reinstated to their old positions.

"The petition explains that after learning its employees were engaging in protected activity, the Employer swiftly retaliated against three of the four members of the union organizing committee," according to the filings. "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 company has had to contend with the NLRB numerous times as it attempts to stem a growing wave of unionization pushes at its many coffee shops. Aside from alleged reprisal firings, the company has also tried to appeal voting deadlines to no avail. It missed a crucial deadline for a legal filing in a significant victory for union organizers in February.

Starbucks has been fighting an uphill battle as workers at stores across the country secure successive unionization victories. Beginning initially in Buffalo, New York, stores from Arizona to Virginia have held successful votes and formed local unions for baristas. Given the strong motivation driving organized labor amid the "great resignation," Starbucks doesn't seem to have any end in sight if it intends to keep resisting unionization.

With the coffee giant now in federal court for union-busting, investors are beginning to sweat at the mounting costs of Starbucks' anti-union crusade. Shares were down 1.41% last week, ending on a sour note with Friday's filing by the NLRB. Shares are down 14.8% since the beginning of April, despite the return of lauded former CEO Howard Schultz on April 4, due to Wall Street's anxieties over the company's growing losses.