There has been a fresh twist to Elon Musk’s £33billion high-profile move to take over social-media platform Twitter.
The company’s board has armed itself against a possible hostile takeover from the leading entrepreneur who is also the world's richest person.
It has adopted a limited-duration shareholder rights plan - also known as a "poison pill".
The move aims to prevent anyone from having more than a 15% stake in the company.
It does this by allowing others to buy additional shares at a discount.
The Twitter board detailed its defence plan to the US Securities and Exchange Commission and put out a statement saying it was needed because of Mr Musk's "unsolicited, non-binding proposal" to acquire the business.
A takeover bid is considered hostile when one firm tries to acquire another against the wishes of that company's management - in Twitter's case, its executive board.
Josh White, a former financial economist for the Securities and Exchange Commission, told the BBC that a poison pill is "one of those last lines of defence against a hostile bid takeover".
"We call it the nuclear option," he said.
Mr White stated that the board has made it clear "that they don't feel like it's a high-enough value for the company".
Because Mr Musk had signalled that he was not willing to negotiate a higher price, the Twitter board went ahead with the poison pill.
Mr White was surprised by Mr Musk's negotiation tactic because if the end game is to acquire the company it might not be the "right approach".
"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," he said.
Mr Musk - Chief Executive of electric car maker Tesla - announced earlier this month that he now has a 9.2% stake in Twitter.
He believes the company is limiting freedom of speech on the platform. He has said his primary motivation would be to expand free speech - a US Constitutional right - on Twitter.
Mr Musk is being advised by the US investment bank Morgan Stanley. Meanwhile, Twitter is being helped by two banks, Goldman Sachs and JP Morgan.
Meanwhile in other news, Brent oil futures were ahead 0.61% at $112.41 a barrel earlier this morning.
The London Stock Exchange is closed today.