UPS has a new risk factor: Amazon - Marketwatch Embracing next-day delivery and competitive wins has boosted business from Amazon, which UPS declared its biggest customer United Parcel Service Inc. has long boasted about its diverse customer base, and had been mum about who its largest customers were, but on Thursday the package delivery giant seemed to embrace the fact that Amazon was the largest customer it’s had in years. “UPS experienced growth from a number of large and [small and medium business] customers, with the growth led by UPS’s largest customer, Amazon,” the company stated in its fourth-quarter earnings report. And that’s not all. For years, UPS has been saying in its annual reports that no single customer accounted for 10% or more of consolidated revenue. “We do not believe the loss of any single customer would materially impair our overall financial condition or results of operations,” the company stated in the “Risk Factors” section of its last seven 10-K filings with the Securities and Exchange Commission.