Frankfurt, Germany - German labour union Verdi has called on workers at online retailer Amazon in Germany to go on strike on Thursday as a long-running pay dispute continues.

"Amazon is refusing talks about a wage agreement," Verdi negotiator Joerg Lauenroth-Mago said in a statement, saying workers at distribution centres in Leipzig and Bad Hersfeld were to walk off the job starting with the morning shift.

Verdi wants Amazon to raise pay for workers at its distribution centres in accordance with collective bargaining agreements across the mail order and retail industry in Germany.

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.

Online retail firms in Germany have struggled to shake off an image of companies that relentlessly drive their workers while paying them relatively little.

Zalando, Europe's biggest online fashion retailer, this week issued a statement in defence of its logistics operations following a critical report by a German undercover journalist.

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

Late last month hundreds of workers walked out at its site in the eastern German city of Leipzig, and several centres were hit by work stoppages in the run-up to Christmas last year.