The drive to unionize Starbucks employees has gathered momentum as workers at two more Seattle locations announced plans to join SB Workers United.

The first Seattle location to unionize was the Denny and Broadway store. Workers there announced their desire for union representation last month. They are now joined by Starbucks' drive-thru location on Westlake, and the store at Fifth and Pike downtown

Some Starbucks workers used to be unionized when the company first formed, decades ago, but the coffee mega-corporation successfully broke the early union. Today, only Starbucks-franchised stores at airports and supermarkets have unionized employees.

The new push for unionization started at two Starbucks stores in Buffalo, New York, where employees voted in December to join Workers United, an affiliate of the Service Employees International Union (SEIU).

The organizing campaign now pits one of the country's biggest corporations against one of its biggest unions. Some 30 Starbucks stores have filed for union representation, according to the National Labor Relations Board (NLRB), the federal agency charged with enforcing labor regulations and supervising union elections. Starbucks has about 9,000 locations nationwide.

Starbucks opposes the unionization efforts of its employees (whom it calls "partners").

"We continue to believe a union is not necessary at Starbucks," Starbucks spokesperson Reggie Borges said in a statement to the Seattle Times. "We believe direct communication between partners has made our company what it is today... We're also going to respect our partners' right to organize."

Starbucks workers say they face severe understaffing in high-pressure stores, work under lax health and safety protocols, and have no input on store policies.

Workers at the Broadway and Denny location on Capitol Hill say the company has begun holding "captive audience" anti-union meetings. In such meetings, the company requires workers to attend propaganda sessions where company spokespeople denounce the union.

Workers at the Denny and Broadway store have also filed an unfair labor practice charge accusing the company of illegally punishing a worker for union activities. Federal labor law protects what is called "concerted action" by workers to get their employers to address grievances.

According to Starbucks corporate spokespeople, the meetings are "an opportunity for partners to be informed," and "we deny any claims of intimidation or union busting."

Having notified the NLRB of their desire to join Workers United, the next step for local Starbucks workers is to hold an NLRB-supervised election. If a majority of the employees vote to be represented by the union, the NLRB will certify the union as their representative in bargaining a contract.