Labor union Verdi has called on workers at online retailer Amazon (AMZN.O) to go on strike at five locations across Germany, as a row over pay and conditions continues.

Verdi said in a statement it had called workers to strike at distribution centers in Bad Hersfeld, Leipzig, Graben, Werne and Rheinberg.

Workers at Bad Hersfeld, Leipzig and Graben will go on strike from Monday to Wednesday, while workers at Werne will strike Monday and Tuesday.

Amazon employs a total of 9,000 warehouse staff at nine distribution centers in Germany, its second-biggest market behind the United States, plus 14,000 seasonal workers.

Verdi wants Amazon to raise pay for workers at its distribution centers in accordance with collective bargaining agreements across the mail order and retail industry in Germany and has organized several stoppages over the past year.

Amazon, however, has rejected the demand, arguing that it regards warehouse staff as logistics workers and says they receive above-average pay by the standards of that industry.