Workers at a Guitar Center store in Pennsylvania have voted to unionize, the fourth location in the music equipment chain to join the Retail, Wholesale and Department Store Union in the past three years.

The union said it won the election on Friday in the Pittsburgh suburb of Monroeville by a vote of nine to five, overcoming what it described as "an intensive anti-union campaign" by the company. Federal officials haven't yet certified the election. If the preliminary results hold, the union will represent 14 employees at the store.

The RWDSU began organizing Guitar Center locations in 2012, when the 260-store chain was entirely non-union. Sales workers came to the union with complaints about their pay rates and the structure of their sales commission. Employees told The Huffington Post in 2013 that they were working more and earning less than they had earlier, leading them to push for unionization.

Guitar Center, now controlled by the private equity firm Ares Management, has pushed back hard against the campaign. Last year, HuffPost profiled a paid consultant, former Teamsters official Michael Ciabattoni, who spent days speaking to workers at a Missouri Guitar Center store about the supposed pitfalls of unionizing. The union lost that election by a single vote.

A Guitar Center spokeswoman didn't respond to a request for comment on the Monroeville election. The company previously told HuffPost that the union campaign was about generating money for the union, and that the company had revised its pay and benefits to address worker complaints.

So far, RWDSU has won elections at four stores -- including flagship locations in New York, Chicago and Las Vegas. The union lost two elections and withdrew a petition to represent workers in at least one store.

Workers are still without a contract at the stores that have been successfully unionized. The general counsel of the National Labor Relations Board, the federal agency that enforces labor law, filed a complaint last year accusing Guitar Center of failing to bargain in good faith with the union. The general counsel also alleged that Guitar Center threatened to cut the benefits of union sympathizers, which would violate labor law. That case is still pending before the board.

Sam Fairchild, a 24-year-old employee at the Monroeville store, said she voted in favor of the union on Friday. A salesperson in the accessories department, Fairchild said she had seen her pay structure change twice since starting work at Guitar Center in May 2014.

"The fact that they can control that without much warning is really not very settling, especially when you are a commission-based employee," Fairchild said. She said she decided to support the union after "realizing that we have nothing to lose."

Fairchild said the workers in Monroeville had regular meetings with Ciabattoni, the consultant, as soon as they filed a petition for a union election. His message, according to Fairchild, was that there were plenty of downsides to unionizing and that employees should think carefully before they vote. (Ciabattoni declined to comment.)

"Everything he said seemed to be accurate to some extent, but he would twist it to make it sound like this wasn't a good thing for us," Fairchild explained. In the end, she said she doesn't think the "anti-union" sessions with employees had much effect on the election.

"I just don't really see a reason why it was necessary," Fairchild said.