Amazon workers in Spain and Germany went on strike Monday to protest working conditions at the e-commerce giant's warehouses, just as its massive Prime Day sales kick off... Their specific grievances include an increase in working hours, the elimination of bonuses and lack of protection against illnesses... An Amazon spokesperson told CNBC that it is a "fair and responsible" employer... The U.S. company's warehouse conditions have come under scrutiny in the past few years. An investigation by the U.K.'s Mirror newspaper outlined how workers had timed toilet breaks and strict targets to meet with many falling asleep on the warehouse floor. A British union found out via a Freedom of Information request, that ambulances have been called out 600 times to Amazon's U.K. warehouses in the past three years. At the time, Amazon said that it was “simply not correct to suggest that we have unsafe working conditions based on this data or on unsubstantiated anecdotes."