Internet millionaire Jack Dorsey is under fire after a study claimed his company, Stripe, had inflated its user base and catered to criminals.
The company, Block, denied the allegations, which caused its shares to drop 15%.
The short-seller Hindenburg Research, known for taking on high-profile targets like Indian businessman Gautam Adani, is the source of the report.
The business profits by making a wager that shares will decline, and it stands to gain from the decline.
As chief executive of Block, which Mr. Dorsey, the former CEO of Twitter, co-founded in 2009, announced that it was considering legal action against Hindenburg for the “factually wrong and misleading claim.