The Guitar Center store is seen in a file photo from Feb. 17, 2004, on Sunset Boulevard in Los Angeles. A California musical instrument retailer has offered to buy Woodwind & Brasswind, one of the country's largest musical instrument sellers, for $37.1 million, subject to higher bids at auction. (AP Photo/Damian Dovarganes, File)

WASHINGTON -- More than a year after its initial election victory at a Guitar Center store, the union representing the chain's first unionized employees is accusing the retailer of bargaining in "bad faith" and trying to purge the union.

The Retail, Wholesale and Department Store Union has filed unfair labor practice charges with the National Labor Relations Board, alleging that Guitar Center has stalled in bargaining talks and "punished" workers who voted in favor of representation. Last year, RWDSU won elections at three Guitar Center stores, although those workers have yet to reach a collective bargaining contract with the company.

On Tuesday, Richard Trumka, the head of the AFL-CIO labor federation, accused Guitar Center ownership of using "shameful" tactics to avoid a contract with the unionized workers.

"The fight against Bain Capital and Ares Management for fair pay and decent health care for the Guitar Center workers is what the labor movement is all about," Trumka said at RWDSU's convention in Orlando, Florida. "The dirty tactics of Bain and Ares have been shameful and ugly. I want every Guitar Center worker to know the entire AFL-CIO and every one of our affiliates stands behind them in their efforts to win a fair contract."

Bain Capital, Mitt Romney's old investment firm, held a controlling stake in the music equipment retailer until April, when it completed a deal handing the reins over to the private equity firm Ares Management.

In an email, Guitar Center spokesman Christopher Bennett called the union's claims "baseless," noting that one worker recently withdrew his charge of an unfair labor practice.

"The RWDSU's continued insistence on filing bogus charges against us and spreading misinformation to our associates and in the media is disappointing and a waste of everyone's time," Bennett said. "For more than a year we have respected the bargaining process and the law in dealing with the union."

Bennett went on, "For 50 years our organization has put musicians and our people first. If the union had any respect for the bargaining process or our associates, they would keep this kind of rhetoric out of the headlines and stop taking cheap shots that nobody takes seriously

As HuffPost reported last year, RWDSU launched an organizing campaign at several Guitar Center stores, where workers had grievances related to job security, health care coverage and the company's wage system for commissioned salespeople. The apparent discontent helped the union notch election victories at shops in New York, Chicago and Las Vegas, with two failed bids at other stores in New York.

The union now alleges that Guitar Center management has made a show of addressing workers' grievances -- but only at the company's non-union stores.

Because unionized workers would be covered by their own contract, it's perfectly normal for a company with both unionized and non-unionized employees to enact new pay-and-benefit policies exclusively for the non-union workforce. But in a letter to the federal labor board, RWDSU said that the company had "refused" to consider the same improvements for the unionized workers at the bargaining table, "all as a method for punishing the RWDSU represented employee for joining the Union."

The labor board is investigating RWDSU's complaints, which it could dismiss or choose to pursue further on behalf of the union.

Phil Andrews, director of the union's retail organizing project, argued that Guitar Center is trying to send a message to other workers who might consider unionizing. "It's a situation where the non-union stores were given a carrot in order to stay away from the union, and the union stores were being punished," Andrews said. "That was the impression they wanted to give."

When it comes to bargaining talks, RWDSU contends that Guitar Center has been dragging its feet in hopes that support for the union will erode before a contract gets signed. In its letter to the labor board, the union accused the company of engaging in "regressive bargaining," changing its stance on wage-and-hour issues and "failing to respond" to proposals from the union.

"It became clear a few months ago to us that their intention was never to negotiate a good contract," Andrews said.

According to National Labor Relations Board filings, Guitar Center is represented by Jackson Lewis, a law firm known for its "union avoidance" work.