The Starbucks Corporation (SBUX  ) continues to lose ground in its fight against labor unions after six additional stores in two states vote to unionize. The firm faces increasing pressure from workers as it continues to try to dissuade employees from unionizing.

Three Virginia stores in Merrifield, Leesburg, and Springfield filed the necessary paperwork with the National Labor Relations Board (NLRB) Friday morning. Earlier last week, three stores in Buffalo, New York, where the first Starbucks unionization drive was held, voted to unionize as well.

While the drive to unionize North America's largest coffee chain has had a string of victories for employees, Starbucks has met the campaign with stiff resistance. So far, employees have reported one-on-one meetings with corporate staff, while the company has attempted to promote a narrative that unionization is "harmful" to its workers. In extreme cases, the company has allegedly fired workers in retaliation, such as a Buffalo area employee fired earlier this month.

At a store in Denver, Colorado, workers recently went on strike against the company for its union-busting efforts. Workers reported threats to cut benefits and hours, baseless disciplinary action, and even spying on organizers.

"I fully expect, unfortunately, that corporate Starbucks will do the same here in Northern Virginia," a Virginia union leader told WAMU in an interview. "So I think it's so important that the community rally around the baristas and the partners who are so important to them and stand up and say, 'Hey, Northern Virginia is a union town.'"

To make matters worse for Starbucks, the NLRB has thus far hindered its efforts to curb unionization efforts legally. Despite attempts to appeal votes in New York and Arizona, the regulator has turned down two appeals; one appeal being dismissed on the grounds of an existing precedent against it and the other due to a late filing. Starbucks likely faces mounting complaints with the NLRB as well, especially if reports of retaliation against workers are investigated in depth.

Starbucks shares slid 8.1% last week, likely due only in part to its increasing union-busting scrutiny. Other factors such as the company's last-minute pullout from Russia and ongoing market disruptions likely had a hand as well.