Twitter Inc. devised a ‘poison pill’ strategy on Friday to block billionaire entrepreneur Elon Musk’s $43 billion cash acquisition attempt.

The rights will become exercisable under the ‘poison pill’ method if someone acquires 15% or more of Twitter’s outstanding common shares in a transaction not approved by the Board. To shield itself against billionaire entrepreneur Elon Musk’s $43 billion cash acquisition offer, the microblogging tech company devised a limited-duration shareholder rights plan. According to Twitter, the rights plan will expire on April 14, 2023.

Musk made the offer in a letter to Twitter’s board of directors on April 13, and his $54.20 per share offer price was revealed in a regulatory filing. It’s a 38 percent premium over Twitter’s April 1 closing price. The last trading day before Musk’s over 9% ownership in the company made public was April 1.

Tesla’s head Elon Musk offers to buy Twitter

On Thursday, the Tesla Inc. chief executive officer Elon Musk offered to buy Twitter at $54.20 a share in cash, valuing the social media company at $43 billion.