Billionaire investor Carl Icahn upped his criticism of Illumina Inc.’s stalled acquisition of Grail Inc., saying in his latest attack that its board set a “new low” in governance by pursuing the deal over antitrust regulators’ objections.

Illumina’s board of directors “elected voluntarily to declare war on antitrust regulators” by closing the transaction before regulators cleared it, Icahn said in a letter published Friday. According to Icahn, its members sought to protect themselves by taking out “an unprecedented level” of additional personal liability protection when the deal closed, Icahn said, citing a Securities and Exchange Commission filing.

San Diego-based Illumina has been dealing with the fallout of moving to close the $7 billion deal for early cancer detection upstart Grail even as regulators moved to block it. Activist investor Icahn is seeking to install three directors on Illumina’s board. Illumina has opposed Icahn’s nominees, saying they’re unqualified.

Illumina did not immediately have comment.

In his letter, Icahn focused on the move by Illumina’s board move to protect itself from blowback related to the acquisition.

“Neither that SEC filing, nor any previous or subsequent SEC filing, press release or public statement by Illumina’s board contains any hint regarding what this agreement is, what it means or why it was adopted,” Icahn said. “And until the directors are deposed, the owners of the company will never truly know what fears prompted them to demand the execution of this agreement as a condition to their acquiescence to management’s maniacal desire to punch antitrust regulators in the face.”