BlackRock's ultimatum to CEOs: Help society or else

Key quote: “Society is demanding that companies, both public and private, serve a social purpose,” Fink writes in the letter. “To prosper over time, every company must not only deliver financial performance, but also show how it makes a positive contribution to society.”

The NY Times' Andrew Ross Sorkin adds: "It may be a watershed moment on Wall Street, one that raises all sorts of questions about the very nature of capitalism."

What's next: Fink says he is hiring additional employees to help monitor how companies respond to his appeal.