(Reuters) - Amazon.com ( AMZN ) 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 ( AMZN ), said the International Brotherhood of Teamsters, which represents about 10,000 workers at 10 of the firm's facilities.

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

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

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

Amazon ( AMZN ) said it does not expect any impact to its operations. The union has "intentionally misled the public" and "threatened, intimidated and attempted to coerce" employees and third-party drivers to join them, a company spokesperson said.

Unionized facilities account for just 1% of Amazon's ( AMZN ) hourly workforce and areas such as New York City have multiple warehouses and smaller delivery depots, which could help Amazon ( AMZN ) blunt any potential strike impact.

Observers said Amazon ( AMZN ) 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.

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

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.

(Reporting by Greg Bensinger in San Francisco and Aditya Soni in Bengaluru; Editing by Arun Koyyur)