Starbucks workers take to the picket line in Seattle and across U.S.

Starbucks’ signature holiday drinks may come with a shot of guilt Thursday for customers sympathetic to the labor movement.

Thousands of Starbucks employees across the U.S. are striking in an ongoing battle with their employer over a host of labor issues.

In Starbucks’ home state, Washington, hundreds of workers across 14 stores walked out Thursday, according to the union representing them.

Starbucks Workers United planned the demonstration on Red Cup Day, a promotional event in which Starbucks gives out free reusable cups to customers who order a signature holiday drink. It’s one of Starbucks’ biggest sales days of the year.

"Basically anyone you talk to who's worked at Red Cup Day will say it's probably one of the worst days of the year," said Elise Mayo, an employee striking outside of the Starbucks Reserve Roastery in Capitol Hill.

Mayo and her coworkers picketed for better benefits, more scheduling control, and most importantly, a contract.

RELATED: Starbucks increases U.S. hourly wages and adds other benefits for non-union workers

The strike appears to have stopped several stores in Seattle from opening because they don't have enough staff. At the Capitol Hill location, store managers appeared to huddle inside the store while dozens of workers picketed on the sidewalk outside.

Eventually the Capitol Hill store did open and a manager and security guard helped customers get in around the picket line.

It’s been two years since the first Starbucks store voted to join Starbucks Workers United, an affiliate of the Service Employees International Union. Hundreds of stores have joined since then, but none has managed to negotiate a contract with Starbucks.

RELATED: Starbucks and union face off in Seattle over negotiation rules

Negotiations have stalled because of a disagreement over whether to allow some union members to participate remotely. The union wants hybrid negotiations, which is a non-starter for Starbucks.

"We again call on Workers United to fulfill their obligations and engage in the work of negotiating first contracts on behalf of the partners they represent," said Starbucks spokesperson Andrew Trull in a statement. "Starbucks remains ready to progress in-person negotiations with the unions certified to represent partners."

Both Starbucks and the union accuse the other of refusing to bargain in good faith.

As contract negotiations stall, Starbucks Workers United is focused on unionizing additional stores to gain more leverage.

"Big picture, I'm hoping that some stores realize that there is power in the union," Mayo said. "That the union is a better way forward and that we can help support them."