https://arstechnica.com/tech-policy/2022/04/twitter-board-fights-musk-takeover-with-unanimous-adoption-of-poison-pill/

Twitter's board of directors approved a poison pill to prevent a hostile takeover in response to Elon Musk's offer to buy the firm. "The company on Friday adopted a so-called poison pill that makes it difficult for him to increase his stake beyond 15 percent," The Wall Street Journal wrote.

In a press release, Twitter said its board unanimously "adopted the Rights Plan following an unsolicited, non-binding proposal to acquire Twitter."