Amazon Prime's Biggest Threat May Be Strikers Inc. (NASDAQ: AMZN) had two problems as it kicked off its big Prime Day. The first is that the site was down during a peak shopping period. The second, and more sinister, is that some workers in Europe used the importance of Prime Day to stage strikes.

Some part of Amazon’s European workforce has protested conditions and wages for more than a year. Also, led by union Ver.di, they have stopped work on other occasions important to Amazon sales. Unlike the website outage, the strikers are not going away.

Amazon has had labor problems for some time. These are not isolated to Europe. There have been related claims about wages and work conditions. Even Amazon’s promise to create 100,000 new jobs in the United States has been met with skepticism. It is not that the new jobs will not materialize. It is that the wages may be so low that a portion of the new workers will live on the edges of the very lower middle class — maybe.

Workers may become a major Achilles heel for Amazon. Workers can stage tactical strikes, as they have done in Europe. Unions can hit Amazon on the days when it is most important to offer seamless customer service. Amazon’s customer service reputation is among its most prized public images.

Strikers are testing Amazon on Prime Day. How much can they disrupt its operations when they come on make-or-break days for the company? The results for Amazon are likely to be troublesome.

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