After Jeff Bezos’s rollicking week parading around the annual Sun Valley conference in his characteristic puffer vest, Monday dawned bright and promising for the Amazon C.E.O. Not only was it Amazon’s Prime Day, a sort of Christmas in July for online shoppers looking to stock up on discounted Amazon-branded Fire TVs and Echo devices, but it also marked Bezos’s ascent into a new class of billionaire—his wealth officially topped out at $150 billion, making him the wealthiest man in modern history, surpassing Microsoft co-founder Bill Gates by a full $55 billion. “It’s such a staggering number,” Cresset Family Office C.E.O. Michael Cole told Bloomberg, in what can only be described as an understatement. And yet, the good news for Bezos seemed to end there. Not only did Prime Day—which, inexplicably, is a 36-hour event that starts Monday and bleeds into Tuesday—get off to a rocky start thanks to glitches, causing Amazon’s stock to sag slightly, but it also coincided with a global strike by Amazon employees over poor working conditions.

Donning masks depicting Bezos’s face with eye holes punched out, workers organized by the group Amazon En Lucha walked out of Amazon’s fulfillment center outside Madrid. Their grievances, according to a statement released by Spain’s Communist Party, include elimination of bonuses, an increase in working hours, and lack of protection from disease. They added that workers had been threatened with dismissal should they take part in the strike, which “demonstrates, once again, the fragmentary and precarious role” into which warehouse workers are forced. Nevertheless, the strike is scheduled to last until Wednesday, and organizers have called on working groups across the continent to join them, garnering support from unions like Italy’s Fisascat. (In a statement to CNBC, Amazon said its compensation package in Madrid is “in the high range of the logistics sector.”)

Amazon’s workers in Poland and Germany are staging their own one-day demonstrations similar to Spain’s three-day strike. In Poland, Amazon workers are reportedly carrying out a work-to-rule demonstration, meaning they’ll do no more than the minimum as required by their contracts. (An Amazon spokeswoman told the Hive that its Polish fulfillment centers were “fully operational” on Tuesday and that “information about strikes in Poland is incorrect.”) In Germany, thousands of workers at six Amazon facilities will reportedly walk off the job for a one-day strike. “The message is clear—while the online giant gets rich, it is saving money on the health of its workers,” Stefanie Nutzenberger, an official with Germany’s Verdi services union, told Reuters. Amazon, meanwhile, said it does not expect many of its 12,000 German workers to join the strike, and that the strike won’t affect Prime Day fulfillment. “Amazon is a fair and responsible employer. We believe in continuous improvement across our network and maintain an open and direct dialogue with associates,” an Amazon spokeswoman told the Hive. “These are good jobs with highly competitive pay, full benefits, and innovative training programs . . . We provide safe and positive working conditions, and encourage anyone to come see for themselves by taking a tour at one of our fulfillment centers.”

This is far from the first time that Amazon has faced backlash from its workers—employees in Italy and Germany went on strike in November over working conditions and pay, and earlier this year Spanish workers walked out in a bid to negotiate contracts. Moreover, the working conditions in Amazon’s fulfillment centers, where workers carry out physically taxing jobs in a high-pressure environment, have long drawn scrutiny: several employees have died in U.S.-based centers, and in the U.K., ambulances have been called 600 times to Amazon’s warehouses in the past three years. An investigation by the U.K.’s Mirror found that workers had timed restroom breaks and strict deadlines to meet. Some fell asleep on the warehouse floor.

Amazon has denied reports of unsafe working conditions, dismissing them as “unsubstantiated anecdotes.” But as Bezos continues to rapidly grow his retail business, erecting warehouses around the world to keep pace with demand, his labor problems aren’t likely to disappear. Nor is the contrast between his “staggering” fortune—which stands to multiply on the success of ventures such as Blue Origin—and the plight of his employees liable to diminish. Amazon’s workers may pack boxes for the richest man in the world, but his wealth doesn’t seem to be making their lives any better.