Amazon.com workers at seven U.S. facilities walked off the job early on Thursday during the holiday shopping rush, aiming to pressure the retailer into contract talks with their union.

Warehouse workers in cities including New York, Atlanta and San Francisco are taking part in the "largest" strike against Amazon, said the International Brotherhood of Teamsters, which represents about 10,000 workers at 10 of the firm's facilities.

The company, however, said it does not expect any effect on its operations during one of the busiest times of the year.

Unions represent only about 1% of the workforce of Amazon, one of the largest companies in the U.S. by market value, and it has multiple locations in many metro areas.

The union had given Amazon a Dec. 15 deadline to begin negotiations and warehouse workers had recently voted to authorize a strike.

"If your package is delayed during the holidays, you can blame Amazon's insatiable greed," Teamsters' General President Sean O'Brien said late on Wednesday.

"We gave Amazon a clear deadline to come to the table and do right by our members. They ignored it. This strike is on them."

The retailer's shares were trading 1.5% higher in premarket hours, a sign that investors do not expect a big disruption from the strike.

The Teamsters have "intentionally misled the public" and "threatened, intimidated and attempted to coerce" employees and third-party drivers to join them, an Amazon spokesperson said on Thursday.

Observers said Amazon was unlikely to come to the table to bargain as that could open the door to more union actions. It employs more than 1.5 million people globally and has said it prefers direct relationships with workers.

Still, the company has responded to recent organization efforts with legal challenges. Amazon has filed objections with the National Labor Relations Board (NLRB) over a 2022 union vote in Staten Island, alleging bias among agency officials.

It also challenged the constitutionality of the NLRB in a September federal lawsuit.

Earlier this year, the company announced a $2.1 billion investment to raise pay for fulfillment and transportation employees in the U.S., increasing base wages for employees by at least $1.50 to around $22 per hour, a roughly 7% increase.