In a letter sent to Yahoo! chairman Roy Bostock on Thursday, Icahn lists the names of the ten people he would like to see replace Yahoo's current board of directors, which include Mark Cuban, who sold Broadcast.com to Yahoo for $5 billion, venture capitalist Adam Dell and CEO and chairman of New Line Cinema, Robert Shaye.

"It is clear to me that the board of directors of Yahoo has acted irrationally and lost the faith of shareholders and Microsoft," says Icahn's letter. "It is quite obvious that Microsoft's bid of $33 per share is a superior alternative to Yahoo's prospects on a standalone basis. I am perplexed by the board's actions. I, and many of your shareholders, strongly believe that a combination between Yahoo and Microsoft would form a dynamic company and more importantly would be a force strong enough to compete with Google on the Internet."

Icahn also disclosed in his letter he had acquired 59 million shares and had sought antitrust clearance from the US Federal Trade Commission to acquire up to about $2.5 billion in Yahoo! Stock.

Icahn has not said whether he has spoken to Steve Ballmer or anyone else at Microsoft regarding his aggressive move.

Earlier this month the software giant retracted its $47.5 billion bid to purchase Yahoo! after last-ditch efforts to negotiate a mutually acceptable sale price proved unsuccessful. Yahoo's board was demanding at least $53 billion, or $37 per share.

Despite the seemingly aggressive stance Icahn has taken on behalf of himself and the other Yahoo! shareholders, he says he hopes the current board will "heed the wishes" of its shareholders and "move expeditiously to negotiate a merger with Microsoft, thereby making a proxy fight unnecessary."