Twitter's board of directors on Friday voted unanimously to use a tactic called a "poison pill" to fend off Elon Musk's attempt to take over the company.
In such a defensive tactic, all Twitter shareholders except Musk could buy more shares at a discount. This would dilute the world's richest person's stake in the company and prevent him from recruiting a majority of shareholders supporting his move.
If Musk's ownership in Twitter grows to 15% or more, the poison pill would go into effect.
Musk, who earlier this week was revealed as the company's largest individual shareholder, with 9.2% of the shares, later offered more than $43 billion, or $54.20 a share, to purchase the entire company.
Musk's offer would provide a substantial premium over Twitter's current stock price of just more than $45 a share.
Free-speech concern expressed
When Musk made his offer, he lamented the company's stance on free speech.
"I believe free speech is a societal imperative for a functioning democracy," Musk said in the filing. "I now realize the company will neither thrive nor serve this societal imperative in its current form."
But instead of putting Musk's offer up for a vote with Twitter shareholders, the company's board said Friday that it would instead offer its shareholders a chance to buy even more shares at a steep discount, effectively diluting the price of the stock.
The plan "will reduce the likelihood that any entity … gains control of Twitter through open market accumulation without paying all shareholders an appropriate control premium," the company said.
The Twitter board's plan will be effective for one year.
As rumors of a poison pill action circulated Thursday, Musk speculated via Twitter on what might happen.
"If the current Twitter board takes actions contrary to shareholder interests, they would be breaching their fiduciary duty," he wrote. "The liability they would thereby assume would be titanic in scale."
One analyst, Dan Ives of Wedbush Securities, told the New York Post that the board's move was a "defensive measure," adding that shareholders would not likely view it positively.
"We believe Musk and his team expected this poker move, which will be perceived as a sign of weakness, not strength, by the Street," Ives told the Post.
Josh White, a former financial economist for the Securities and Exchange Commission, told BBC that Musk's negotiation tactics might not be the "right approach" if Musk wants to acquire the company.
"I actually think if he was truly serious about the takeover attempt, he would have started at a price and left the window open for negotiation," White said.
Edward Rock, who teaches corporate law and governance at New York University's law school, also had doubts about whether Musk was serious about buying Twitter.
As Rock told NPR, Musk can show he is serious by revealing how he plans to finance the takeover, which he did not show in his SEC filing, or launch a proxy contest to replace Twitter board members in response to its poison pill.
If Musk fails to do so, Rock said, "he's not going to acquire the company, and people can just write it off like some of his other Twitter storms."
Some information for this report came from The Associated Press.