Dissident shareholder Carl Icahn aims to block an alliance by Time Warner Inc.'s (TWX) America Online unit and Web search leader Google Inc. (GOOG), saying the pact could undermine a potential merger between AOL and a Google rival, the billionaire investor said Monday.

In a letter to Time Warner's board of directors, Icahn said that the company appeared to be on the verge of a "disastrous decision" following reports it is in talks to sell a 5 percent stake of its AOL Internet unit to Google Inc.

Icahn, whose group has a 3.1 percent stake in Time Warner, said he was concerned a Google pact may preclude a merger or other type of deal with the likes of eBay Inc. (EBAY), Yahoo Inc. (YHOO), IAC/InterActiveCorp (IACI), or Microsoft Corp. (MSFT).

"Like all shareholders, I am not opposed to Time Warner entering into an AOL transaction that creates long-term value," Icahn wrote. "However, I am deeply concerned that the Time Warner Board may be on the verge of making a disastrous decision concerning an agreement with Google," he said.

The opposition by Icahn to a stepped-up Web search and advertising alliance between AOL-Google slowed a renewed surge in the price of Google shares Monday, which hit a new intraday record high of $446.21.

The stock, which had been trading up 3.7 percent on the day slid back to a levels around $442, up 2.75 percent. Meanwhile, Time Warner shares gained 13 cents, or 0.7 percent to $18.13.

Icahn, who has said he is waging an "all-out proxy battle" to force Time Warner to step up asset sales and streamlining, cited a recent report by Goldman Sachs that argued that Google may not be the best long-term partner for America Online.