It's a supreme court decision that is allowing Amazon to do this [0].
TL;DR the decision is solely on if the "activities are an intrinsic element of the employee’s primary job duties and one that cannot be skipped" and since they were "hired to retrieve products from warehouse shelves, not to undergo security screenings, and the company could eliminate the screenings altogether without impairing the employees’ ability to complete their work" Amazon/warehouse contractor didn't have to pay for it.
[0] https://www.idfa.org/news-views/headline-news/article/2014/1...