Twitter on Friday said that its board of directors has unanimously decided to adopt a “poison pill” strategy after Tesla Chief Executive Officer Elon Musk offered to buy the social media platform for $43.4 billion, or over Rs 3.31 lakh crore.

A poison pill defense strategy, officially known as the shareholder rights plan, allows existing shareholders to purchase additional shares in a company at a discount. It makes the buyout costly for the other party, effectively diluting its ownership interest. The mechanism, developed in the 1980s, is commonly adopted by companies in hostile takeover situations.

Twitter announced that the plan would take effect if Musk’s stake, which is currently at 9%, grows to 15% or more.

“The Rights Plan is intended to enable all shareholders to realise the full value of their investment in Twitter,” a press release by the social media company said. “The Rights Plan will reduce the likelihood that any entity, person or group gains control of Twitter through open market accumulation without paying all shareholders an appropriate control premium or without providing the board sufficient time to make informed judgments and take actions that are in the best interests of shareholders.”

However, Twitter added that the “poison pill” strategy will not prevent the board of directors from engaging with parties or accepting an acquisition proposal that it considers would be in the best interest of the company and its shareholders. It said the strategy will expire on April 14, 2023.

On April 4, Musk had bought a 9.2% stake in Twitter, which made him the biggest shareholder in the company at the time. The Tesla chief, however, decided not to join the board of directors of the social media platform. On April 13, he made an offer to buy the company.

Twitter’s board of directors had said that it will review Musk’s Securities and Exchange Commission filing, calling it an “unsolicited non-binding offer”. The board had said it will decide its next steps in the “best interest of the company and all Twitter stockholders”.

Meanwhile, Musk on Thursday said he was not sure whether his takeover bid for Twitter will be successful, the BBC reported. “I am not sure that I will actually be able to acquire it,” Musk said during an event in Vancouver.

He, however, added that he had a “Plan B” if his bid for Twitter was rejected, but gave no further details.

Musk also said that Twitter should be more open and transparent. “I think it is very important for there to be an inclusive arena for free speech,” he said.