Workers in online retailer Amazon's warehouses in Germany started a three-day strike on Monday, asking for higher payment and better working conditions.

About 2,300 workers in five of Amazon's nine German warehouses participated the strike, said union Ver.di which organized the action, adding that the strike would extend to six warehouses on Tuesday and last until evening shift on Wednesday.

Ver.di accused the U.S. online retailer of blocking a collective bargain over payment and called the strike "a great success" which "increased pressure on Amazon."

Workers in Amazon warehouses said they received lower wages than others in retail and mail-order jobs. While Amazon was only willing to regard the workers as logistic staff and insisted that it had offered wages above the industry average.

The strike came as consumers in Germany order gifts for the coming Christmas. German retailers' association HDE forecast that retail sales would increase annually by 1.2 percent to 85.5 billion euros (about 106.3 billion U.S. dollars) in Christmas season this year. Among them, 10 billion euros would be contributed by online business.

Amazon, which employed more than 9,000 full-time workers in Germany, insisted that the strike would not disturb its business and customers could expect punctual deliveries. Endit