The Federal Trade Commission has given activist investor Carl Icahn approval to purchase a large chunk of Yahoo stock, it said on Friday.

The FTC is required under current rules to give its approval to large purchases of stock, and for Carl Icahn, that approval came Friday (PDF available here). Icahn currently owns a little over four percent of Yahoo, valued at around $1 billion USD.

With the additional purchase of stock, which totals about $1.5 billion, Icahn will own close to 11% of Yahoo, which gives him quite a bit of say in the business of the company.

Yahoo is prepping itself for the fight, having already delayed its annual shareholders meeting to later in July. It is also apparently talking to Microsoft about a deal that essentially stops just short of a buyout.

Icahn, long a thorn in many a troubled company's side, seems to be successful in rallying shareholder discontent over Yahoo's direction. Including his own slate of directors, as many as 30 people could be vying for positions on Yahoo's board.