They are also striking at six warehouses in Germany, threatening to disrupt one of the year's busiest shopping days.

Like the rest of Europe, Italians in recent years have embraced the U.S. tradition of Black Friday, a day of heavy discounting by retailers on the day after Thanksgiving.

Unions said in a statement more than 500 Amazon workers at the Piacenza site in northern Italy had agreed to strike following a failure to negotiate bonuses with the company.

Workers have also decided not to do any overtime until Dec. 31, covering the peak season for the online retailer which hires temporary workers during this period.

Amazon employs around 1,600 people on a permanent basis at the Piacenza site, the first it built in the country after launching its Italian website in 2010.

The Verdi trade union in Germany said Amazon employees would also strike on Friday at six distribution centres in the country as part of a long-running dispute over pay and conditions. ■