Workers at Amazon's main distribution hub in Italy are planning their first-ever strike for Friday, trade unions said, while 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.