• Amazon workers at several warehouses went on strike on Thursday.
• The strike comes in the middle of Amazon's key holiday shopping and shipping season.
• Amazon said that it wasn't seeing an impact on its operations.

Amazon workers at seven Amazon fulfillment centers went on strike Thursday, though the retailer said it wasn't seeing effects on its holiday delivery operations.

The workers are walking off the job after Amazon refused to bargain with them over a contract, according to a statement from the Teamsters, which represents the employees.

The strike will affect three Amazon fulfillment centers in Southern California as well as one each in New York, Atlanta, San Francisco, and Illinois, according to the Teamsters. The union said it will also set up picket lines at other Amazon facilities.

The action comes in the middle of the key holiday shopping season. Amazon's highest quarterly revenue has historically come during the final three months of the year. This year, that period included the company's October Prime Day as well as deals for Black Friday.

"If your package is delayed during the holidays, you can blame Amazon's insatiable greed," Sean O'Brien, general president of the Teamsters, said in the statement.

O'Brien said that the Teamsters "gave Amazon a clear deadline to come to the table and do right by our members."

"They ignored it," he added.

An Amazon spokesperson said Thursday morning that the company hasn't seen its operations affected by the strike.

Spokesperson Kelly Nantel said in a statement that the Teamsters recruited non-employees to participate in the strike and intimidate Amazon employees. When Business Insider asked for evidence of those claims, an Amazon spokesperson said, "We know our employees, and we know they are not out there. Our employees repeatedly claim to management that they experience harassment from activists."

"We appreciate all our team's great work to serve their customers and communities, and are continuing to focus on getting customers their holiday orders," Nantel said.

Workers at some Starbucks stores were also preparing for a potential strike this week. On Tuesday, a union representing about 10,000 baristas said its members had voted to authorize a strike, though negotiations with Starbucks have continued and no strike date has been set.

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