Amazon workers in Germany, Spain, Italy and the U.K. walked off the job on Black Friday, mixing labor unrest with the start of the biggest shopping season of the year.

Close to 90 percent of the workers — some 1,600 employees, according to Business Insider — participated in the walkout at Spain’s largest Amazon warehouse in San Fernando de Henares near Madrid, and will continue to strike Saturday, Reuters reported.

Some 620 workers also walked out at German distribution centers in Bad Hersfeld and Rheinberg. But Amazon officials said most staff continued working and customer service was unaffected, according to Reuters.

The 24-hour German strike was organized by the Ver.di services union, which is demanding better pay and safe and healthy working conditions.

“We are entering the end of year spurt, the most stressful time for employees,” union representative Mechthild Middeke told Reuters. “Especially on a day like Black Friday, employees should be the central focus.”

The union, which has been pushing for years for higher pay, says Amazon workers receive lower wages than others in retail and mail-order jobs. But Amazon claims the work sites are logistics centers and pay well for that sector, The Associated Press reported. German staff earn a starting pay of the equivalent of $12.23 an hour, according to Reuters.

An early statement from British union GMB said hundreds were expected to strike at five locations across the U.K. Friday to protest “inhuman conditions” at Amazon warehouses. GMB claims that ambulances have been called 600 times to Amazon warehouses in the past three years ending in May to attend to worker injuries on the job.

“The conditions our members at Amazon are working under are frankly inhuman,” said a statement by GMB General Secretary Tim Roache. “They are breaking bones, being knocked unconscious and being taken away in ambulances.

He added: “We’re standing up and saying enough is enough. These are people making Amazon its money. People with kids, homes, bills to pay — they’re not robots. Jeff Bezos is the richest bloke on the planet; he can afford to sort this out.”

Amazon announced last month that it would raise its minimum wage to $15 an hour in the U.S., but then eliminated several financial perks apparently as a way to fund the hourly raises.