Billionaire Elon Musk was sued by Twitter Inc. investors for delayed disclosure of his stake in the social media company in a complaint filed on Wednesday in California federal court.

The investors said Musk saved himself $156 million by failing to disclose that he had purchased more than 5% of Twitter by March 14. He continued to buy stock after that, and ultimately disclosed in early April that he owned 9.2% of the company.

"By delaying his disclosure of his stake in Twitter, Musk engaged in market manipulation and bought Twitter stock at an artificially low price," said the investors, led by Virginia resident William Heresniak.

The suit comes after Musk, the owner of electric carmaker Tesla Inc, said he planned to take over Twitter for $44 billion.