Sophia Lewis’s career was on the rise. Then she began telling her bosses about questionable sales practices. ‘Things started going downhill.’

Sophia Lewis thought she would build a long career at American Express Co. A few years in, though, she was telling her bosses that something was wrong.
Ms. Lewis said she saw some AmEx employees routinely submit corporate card applications without verifying the companies financial information, pocketing commissions each time. Beginning in 2018, Ms. Lewis said, she alerted higher-ups about those complaints. But AmEx, she said, had created a culture where employees can get rewarded for breaking rules.