(NewsNation) — Nearly 10,000 Amazon workers who are part of the Teamsters union are striking across the United States ahead of the Christmas holiday.

Teamsters are demanding more money for workers and claim that Amazon officials have not done enough to fix workplace safety issues. Amazon has denied the claims.

Picket lines are being seen in cities like New York, Chicago and Atlanta as workers are walking off the job as the holiday rush to get packages delivered across the country heats up.

In suburban Chicago, about 400 Teamster drivers work at a facility where some employees are encouraging their colleagues to join the picket lines. The main demand is better pay. Drivers claim they are living paycheck to paycheck.

Workers are also upset with how quickly they must process packages at Amazon fulfillment centers, citing a study that showed that workplace injuries at Amazon are double that of the industry standard. This week, a report released by the majority staff for the Senate Committee on Health, Education, Labor and Pensions, found that Amazon accepted employee injuries as part of the “cost of doing business.”

Amazon responded by saying that the committee’s chair, Vermont independent Sen. Bernie Sanders is “misleading the American public.”

Teamsters’ officials also argue Amazon management did not come to the bargaining table. Amazon executives maintain that the Teamsters are not representative of all of the company’s drivers.

Amazon pays a driver service which in turn, provides about 7,000 independently contracted drivers for Amazon, which says the drivers are not Amazon employees. Those drivers, the company says, represent less than 1% of its workforce.