Activist investor Carl Icahn is preparing to launch a proxy fight at Illumina, seeking three board seats, prompted by the biotech company's $8 billion acquisition of cancer screening start-up Grail, which Icahn says is now costing the company $800 million per year, according to reports.

Icahn has nominated Vincent Intrieri, Jesse Lynn, and Andrew Teno to Illumina's board and claims that three shareholder representatives are needed to put an end to what he calls "reckless decision-making."

Shares in Illumina surged more than 20% on Monday after Icahn sent a letter to the company's shareholders alleging that the "ill-advised" Grail purchase in 2021 had wiped out $50 billion of the genome sequencing company's value.

Illumina's market capitalisation slumped from $75 billion in August 2021 when it acquired Grail to just over $30 billion last month.

According to a securities filing, Icahn, who has said he tried to strike a deal with Illumina before starting the proxy battle, owned a 1.4 per cent stake in the company worth $427 million as of last week’s close.