The employee complaint program, which started in 2015, violated laws prohibiting management-run labor organizations that resemble unions, Sharon Levinson, a judge for the National Labor Relation Board, said in a 47-page decision.

The ruling comes as labor relations in the telecommunications industry face increasing strains. About 40,000 Verizon workers went on strike for seven weeks last year for better wages and extra job security while 17,000 AT&T workers went on a one-day strike last month amid negotiations over an expired contract.

Workers across the industry are upset about reduced health benefits, stagnant pay, and jobs being outsourced or moved overseas. Meanwhile, carriers are trying to please investors who want cost cuts as the wired telephone business continues to shrink and growth in the wireless markets has stalled.

The NLRB judge’s ruling came after T-Mobile call center workers who sought to join the Communications Workers of America union last year complained that T-Mobile was thwarting their efforts. By appointing workers to hear complaints about job conditions under the T-Voice program, the company was usurping a role reserved for employee-run unions, the judge found.

T-Mobile declined to comment. But CEO John Legere responded on Twitter, calling the decision “ludicrous” and saying T-Mobile would appeal. 

The CWA has been trying to unionize T-Mobile’s 50,000 workers for many years. For example, last year, the union opened its first official field office in Wichita, Kan., near a T-Mobile call center. Additionally, a group of workers organized as T-Mobile Workers United has met with management and successfully pressed for better working conditions in some locations, but without a collectively bargained contract.

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But thus far, CWA’s efforts to get workers to join the union and press for a contract have largely been unsuccessful, as only a few dozen T-Mobile (TMUS) employees in New York and Connecticut work under a union contract.

T-Mobile had insisted that the T-Voice program was aimed at improving customer service, not labor relations, and only accidentally responded to a few complaints about work conditions. But Judge Levinson cited numerous examples of the company reacting to worker complaints it gathered through the program including fixing scheduling problems, modifying employee rewards programs, and adjusting training benefits.

Verizon strike hurt sales:

The T-Voice controversy is not the first time T-Mobile has had trouble with labor relations. Two years ago, it lost several cases before the NLRB concerning a crackdown on employees who wanted to discuss starting a union, improper treatment of employees who wanted to discuss internal misconduct, and an employee who was fired for reporting safety concerns.

Under federal law dating back to the 1930s, employers are prohibited from establishing company dominated unions for their workers. The aim is to prevent companies from confusing workers who may be interested in forming an independent union.