Federal authorities are investigating the release of wealthy Americans’ tax information, Internal Revenue Service Commissioner Charles Rettig said Tuesday.

ProPublica, a nonprofit news organization, published details about the reported income and tax payments of some of the richest Americans, including Amazon.com Inc. Chief Executive Officer Jeff Bezos and Berkshire Hathaway Inc. CEO Warren Buffett.

Taxpayer information is confidential, and there are potential criminal penalties for IRS employees or others who release such information. Mr. Rettig told lawmakers that there were internal and external investigations beginning, with potential prosecutions to follow.

“I share the concerns of every American for the sensitive and private nature and confidential nature of the information the IRS receives,” he said during a Senate Finance Committee hearing that had been scheduled before the information was released. “Trust and confidence in the Internal Revenue Service is sort of the bedrock of asking people and requiring people to provide financial information.”