Activist investor Carl Icahn owns a substantial holding in PC maker Dell and is opposing the proposed deal to take the company private, it emerged yesterday. 

In a letter to Dell's board of directors earlier this week, Icahn said the proposed $24 billion takeover bid from founder Michael Dell and private equity firm Silver Lake "substantially undervalues the company".

If that deal is turned down by shareholders, Icahn says he will finance an alternative offer that values the company at $39 billion – a 67% increase. If the board were to decline that offer, Icahn has threatend "years of litigation" and would seek to have the company's directors replaced.

The letter was revealed yesterday in a public filing by Dell, in which the company welcomed Icahn's interest.

“The Special Committee is currently conducting a robust ‘go-shop’ process to determine if there are third parties interested in proposing alternative transactions that could be superior for Dell’s public shareholders to the going-private transaction — and we welcome Carl Icahn and all other interested parties to participate in that process," Dell said in its filing.

"Evercore Partners, an independent financial advisor to the Special Committee, is actively soliciting third parties to determine their potential interest and is incentivized to find a superior proposal if one exists," it said.

A number of Dell's investors have opposed the buyout offer, including the company's second and third-largest investors Southeastern Asset Management and T Rowe Price.