Azealia Banks has reignited her feud with billionaire Elon Musk after he attacked her credibility in a Tesla shareholder lawsuit.

Investors in the electric car firm are suing its founder over a tweet he wrote claiming he was taking the firm into private ownership, as they allege he manipulated the market and cost them millions of dollars.

Their lawyers have tried to subpoena Banks and Musk's then girlfriend Grimes, as the rapper claimed to have been present at his home for a recording session that was abandoned due to the fallout from his social media activity.

In a filing objecting to the 212 hitmaker's being subpoenaed as a witness obtained by Bloomberg, the tech entrepreneur's lawyers called her credibility into question, prompting her to lash out on Instagram.

"They are still slighting me like I don't have plenty more dirt to spill on Elon," she wrote in a since deleted post screengrabbed and published by The Guardian. "This is going to get extremely ugly. I may be a lot of things but a liar is not one of them. Elon will learn very soon who is more powerful of us two."

Banks also alleged that Musk and his team had taken her phone and "tried tampering" with evidence.

The New York Times, Gizmodo and Business Insider, all of whom interviewed either the hip-hop star or businessman about the bizarre incident, have also been subpoenaed.

The Tesla founder's lawyer Dean Kristy wrote in his filing on Friday (04Jan19) that the 27-year-old musician had a "history of making bold and sometimes unverified claims" against stars including Beyonce and Russell Crowe, referring to allegations she has made about both stars on social media.