Here are a few of the most relevant writings on CEO activism.
Assessing the Impact of CEO Activism by Aaron Chatterji, Michael W. Toffel
The New CEO Activists, by Aaron Chatterji, Michael W. Toffel in Harvard Business Review
When CEOs Should Speak Up on Polarizing Issues by Alison Taylor, Harvard Business Review
2018 CEO Activism Survey by David F. Larcker and Brian Tayan, Stanford Graduate Business School