Hundreds of workers, part of labor union Verdi,  at German warehouses of U.S. online retailer Amazon went on strike Monday as part of a long-running dispute concerning better pay and working conditions.

Monday's strike, reportedly consisting of workers from six of the nine Amazon warehouses in Germany, marks the third consecutive year Verdi has called on Amazon employees to strike before Christmas, according to CNN.

A Verdi spokeswoman said the union expects the strike to see numbers similar to what was observed in previous years. For example, last year Verdi reported almost 2,300 workers at five of Amazon's nine distribution centers went on strike Dec. 15, 2014 before extending to a sixth center the next day, according to Reuters.

However, an Amazon spokeswoman disputed Verdi's forecast, saying only a minority of staff were on strike and it would have no impact on its ability to deliver packages during the holiday season.

"There is absolutely no impact on our customer delivery promise. The vast majority of our employees are working," she said, noting that Amazon has a total of 29 warehouses across Europe that it uses to fulfill orders.

Verdi argues that Amazon employees suffer from excessive pressure, rigid workplace controls and high sickness rates, reported Reuters. Most recently the union has been embroiled in a debate against Amazon over its plans to have employees work during busy periods on Sunday.

Amazon has dismissed these accusations and argued that its warehouse employees' entry wages were about $10.86 gross per hour, which it describes as an "attractive" compensation deal.

Amazon has received praise for being the most valuable retailer in the world, however this praise comes as its employees complain about poor conditions and low pay, with some going so far as filing lawsuits.