By adopting the business plan, also known as a "limited duration shareholders rights", Twitter may now open the door for other partners to buy discounted shares.
The poison pill not only blocks current shareholders attempt to sell their stake, but also allows board members to determine the case of Musk's grand offer.
"It is a predictable defensive measure for the board to go down that will not be viewed positively by shareholders given the potential dilution and acquisition-unfriendly move," Wedbush analyst Dan Ives said.
Musk is reportedly the world's wealthiest man, currently worth $265 billion after selling majority of his shares in origin electric car company Tesla.
The 50-year-old from South Africa also controls satellite company SpaceX, involved in space exploration at a similar level to rival and Amazon CEO Jeff Bezos.
Get the latest breaking news from SCA newsrooms around Australia. Short, simple and everything you need to know.
Download LiSTNR and enjoy a new world of audio. All your favourite shows and stations in one library.