PARIS—Digital payment services developed by U.S. tech giants such as Apple and Alphabet’s Google risk reinforcing their market power by giving them greater sway over consumers’ data, France’s antitrust authority said on Thursday. The remarks, part of a 127-page opinion, follow a one-year inquiry into new payment technologies and shine a light on the watchdog’s views in the field, marked by a proliferation of smartphone banking apps, such as Britain’s Revolut and Germany’s N26. In its opinion, the French watchdog says that Apple, Google, and Amazon’s payment services enjoy important competitive advantages thanks to the large number of users their platforms have attracted and the trove of data they’ve collected. These allow them to better evaluate their users’ financial health and to adapt their offers, including by estimating the maximum price a customer is willing to pay for a product or a service. “Near Field Communication” (NFC) technology, the most-used …