Starbucks union members vote to authorize strike before the final bargaining session of the year.

• The union representing Starbucks employees has voted to authorize a strike in pursuit of a contract with the coffee company.
• The last scheduled bargaining session of the year will take place with both sides present.
• In late February, Starbucks and the union declared that they would establish a "base agreement" on how to achieve a collective bargaining agreement for stores.

The union baristas of Starbucks have voted to authorize a strike, with 98% of the workers supporting the move, according to Workers United.

On Tuesday, bargaining delegates will reconvene with Starbucks for the final negotiation session of the year, aiming to establish a "foundational framework." According to a press release from Workers United, the union and Starbucks have spent hundreds of hours at the bargaining table this year, and both sides have presented numerous proposed agreements.

Despite the union's demands, Starbucks has not yet presented a comprehensive plan to resolve the hundreds of unfair labor practice cases and improve barista pay and benefits.

The strike authorization indicates that relations between the two sides may be cooling again, after they had thawed in late February when both parties said they found a "constructive path forward" through mediation. Prior to that point, Starbucks had fought the union boom that had swept across its company-owned locations for more than two years. The company's efforts to suppress the union movement resulted in backlash from some consumers and lawmakers, ultimately leading to former CEO Howard Schultz testifying on Capitol Hill.

In his first weeks as Starbucks CEO, Brian Niccol pledged to engage in constructive negotiations with the union.

On Monday, Niccol announced that the company would double its paid parental leave, starting in March. Meanwhile, baristas are expected to receive a smaller annual pay hike next year than they have in previous years, following a sales slump at its U.S. locations.

Since the first unionization elections in Buffalo three years ago, over 500 Starbucks cafes have voted to unionize under Workers United.

CNBC did not receive an immediate response from a Starbucks representative when requesting a comment.