BERLIN (AP) — Workers at Amazon distribution centers in Germany have gone on strike for better pay on Black Friday, one of the busiest days of the year for the online retailer.

Union ver.di said Friday that the walkouts began overnight at six distribution centers across the country, with some due to last until Tuesday.

Union representative Orhan Akman said Amazon staff want to send a signal that their work can’t be bought with the kind of extreme discounts Amazon offers around this time of the year.

Akman also accused the company of putting “extreme pressure” on staff that’s causing some to fall ill.