(NewsNation) — Starbucks union employees will strike at locations in Los Angeles, Chicago and Seattle Friday morning, which could impact holiday sales, in a pre-Christmas push for increased wages and better schedules.

Workers United, which represents employees from more than 500 Starbucks stores nationwide, said the walkouts could reach hundreds of stores by Dec. 24 if a deal with the company isn’t reached, Reuters reported.

The union has been negotiating with Starbucks over wages, staffing and schedules. Starbucks said union representatives prematurely ended their bargaining session this week, according to Reuters.

Ninety-eight percent of union members voted Tuesday to authorize the strike.

“Starbucks can’t get back on track as a company until it finalizes a fair contract that invests in its workforce,” said Silvia Baldwin, a Philadelphia barista and union bargaining delegate, in a news release. “Right now, I’m making $16.50 an hour. Meanwhile, Brian Niccol’s compensation package is worth $57,000 an hour.”

Niccol is Starbucks’ chairman and CEO, joining the company in September.

Amazon workers, similarly, went on strike this week at seven U.S. facilities, demanding better pay and safer working conditions.