Icahn wanted the vote on Michael Dell's offer and the company's annual meeting to be scheduled the same day so he could oust the board. But he noted in his shareholder letter that a Delaware judge ruled that the gap between Thursday's vote and the annual meeting set for next month was legal.
The investor said he believed that combining those meetings would have pressured Michael Dell and Silver Lake to raise his offer even more.
Icahn also had complained that Dell's directors unfairly favored Michael Dell by moving up the investment date that makes a shareholder eligible to vote and by counting only votes that were actually cast, excluding those controlled by Michael Dell's group.
Dell's board moved up the cutoff date for voting eligibility to Aug. 13 from June 3. The created a new pool of voters, including many investors who bought the stock in the past few months and stand to profit from the sweetened offer.
The vote on Michael Dell's buyout offer had already been delayed a few times as Michael Dell's group tried to rally support. That prompted Icahn to compare the company to a dictatorship.
"We jokingly ask, 'What's the difference between Dell and a dictatorship?," he said in his shareholder letter. "The answer: Most functioning dictatorships only need to postpone the vote once to win."
Dell spokesman David Frink declined to comment on Icahn's letter.
Icahn's decision to end his opposition makes shareholder approval of Michael Dell's latest offer virtually certain, according to Carr Lanphier, an analyst who follows the company for Morningstar.
"(Icahn) was the real driving force behind the opposition," Lanphier said.
If shareholders accept Michael Dell's bid, the company expects the deal to close later in its third quarter, which ends next month.
Dell shares rose a penny to $13.85 in Monday afternoon trading, while the Nasdaq exchange rose more than 1 percent.
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