See Poison Pill (https://corporatefinanceinstitute.com/resources/knowledge/deals/poison-pill-shareholder-rights-plan/ https://corporatefinanceinstitute.com/reso

See Poison Pill (https://corporatefinanceinstitute.com/resources/knowledge/deals/poison-pill-shareholder-rights-plan/ https://corporatefinanceinstitute.com/resources/knowledge/de...) tldr; A poison pill is a shareholder rights plan or other strategy that can be used to fend off an acquirer or force them to the negotiating table. Cited article has examples of hostile takeover bids thwarted using Poison Pills from '80s used in the Oil industry to Netflix in 2012. It is not a total ban on acquisition but more of a strategy to help the board with a negotiating tool.