Renowned billionaire activist investor Carl Icahn has launched a securities class and derivative action against Illumina Inc. and its board of directors, accusing them of violating their fiduciary responsibilities towards stockholders. This move follows Icahn's extensive campaign opposing Illumina's $8 billion reacquisition of cancer testing firm Grail Inc.

While the complaint filed in Delaware's Chancery Court by Icahn's firm, Icahn Partners LP, remains unavailable as of Tuesday, his attorneys revealed in a public supplement that there was "good cause" for the suit to be assigned to a chancellor or vice chancellor rather than a magistrate in chancery. The legal action is on behalf of Illumina and all its stockholders.

Icahn initiated a proxy battle in March to challenge Illumina's decision to repurchase Grail. He publicly criticized this decision as "ill-advised" and "frankly inexplicable."

In a statement shared with Law360, Icahn expressed that throughout his career as an activist, he has never had to resort to suing a board of directors in this manner. He took this step due to the board's "unconscionable and egregious actions" related to the Grail acquisition, which occurred without regulatory approval, potentially putting Illumina at risk.

While the lawsuit was filed under seal, Icahn noted, "I continue to believe in the company's long-term potential, and I have full faith in Illumina's new CEO and its employees."

Illumina stated it is currently reviewing the complaint.

Illumina established Grail, spun it off, and later repurchased it in 2020. Icahn's advocacy led to the Federal Trade Commission ordering the dissolution of the deal in April, with European regulators also scrutinizing the transaction.

Icahn had previously called for the removal of Illumina CEO Francis deSouza, who resigned in June. Additionally, he successfully orchestrated the removal of Illumina's former board chair, John Thompson, and the election of one of his nominees, Andrew Teno, as a board member.

Illumina has appealed the FTC's decision, emphasizing that the Grail acquisition was essential for widespread adoption of its cancer tests. Nevertheless, the company has indicated that it will "move expeditiously" to divest Grail if it doesn't succeed in the FTC or European cases.

Icahn voiced support for Illumina's new CEO, Jacob Thaysen, on X (formerly Twitter) last month.

Earlier this year, Icahn Enterprises disclosed that federal prosecutors had initiated an investigation based on a short seller's report alleging inflated business value. The company is cooperating with the inquiry initiated by the U.S. Attorney's Office for the Southern District of New York on May 3.

Icahn and other plaintiffs are represented by C. Barr Flinn and M. Paige Valeski of Young Conaway Stargatt & Taylor LLP, along with Michael A. Hanin, Christian T. Becker, Andrew L. Schwartz, and Andrew M. Meerwarth of Kasowitz Benson Torres LLP.

Information regarding counsel for the defendants was not immediately available as of Tuesday.