Twitter has announced a limited-duration shareholder rights plan that may thwart billionaire entrepreneur Elon Musk’s attempts to take over the company. Musk, the chief executive of Tesla and the world’s richest person, had offered to buy the social media platform for $43.4bn, arguing he wanted to release its “extraordinary potential” to support free speech and democracy across the world. In response, Twitter’s board on Friday unanimously approved a plan that would allow existing shareholders to buy stocks at a substantial discount in order to dilute the holdings of new investors. The method, known as a “poison pill” in the finance world, suggests Twitter will fight Musk to prevent a hostile takeover. It would go into effect if a shareholder were to acquire more than 15% of the company in a deal not approved by the board and expires 14 April 2023. “The Rights Plan does not prevent the Board from engaging with parties or accepting an acquisition proposal if the Board believes that it is in the best interests of Twitter and its shareholders,” Twitter said in a statement. Twitter’s response is the latest twist in a saga between the billionaire and the social media site, of which Musk himself is an avid user. Musk revealed on 4 April that he had become the largest stakeholder in Twitter, quietly scooping up 9.2% stake in the company in recent months. He was then offered a seat on the board, a move that was abruptly reversed after Musk declined. Employees at the social media firm have expressed concern about what a Musk-controlled company would look like, and frustration that details of the acquisition are still unclear. In an all-hands meeting on Thursday, CEO Parag Agrawal reportedly assured employees the company was not being “held hostage” by the takeover saga. He encouraged employees to remain focused and told them “we as employees control what happens,” Reuters reported. Few experts are willing to speculate what will happen next, but a bidding war could be on the horizon. On Friday, Reuters reported that the buyout firm Thoma Bravo LP had contacted Twitter to express interest in making a competing offer to Musk’s bid. Shortly after Musk shared he had become the largest shareholder in Twitter, Vanguard group purchased more shares and surpassed him, now owning 10.3% of the company. Jack Dorsey, Twitter founder and former CEO, noted in a tweet on Friday that such surprise purchases are always a risk for the company. “As a public company, Twitter has always been ‘for sale’,” he said. “That’s the real issue.” Musk is already facing legal action for his Twitter purchases, with one investor suing the Tesla executive in a potential class action lawsuit for failing to disclose his buy-up of shares before the required deadline to do so. The lawsuit comes as Musk faces a number of investigations by the Securities and Exchange Commission for his investment activities, including insider trading allegations related to his own tweets.