Activist investor Carl Icahn stepped back in its efforts to convince Apple shareholders demand an increased stock buyback plan, following a proxy adviser's call against his proposal. In a letter to Apple shareholders on Monday, Icahn wrote that he had decided to ditch his nonbinding proposal, "especially when the company is already so close to fulfilling our requested repurchase target."

Icahn has been asking Apple to boost its plans for a stock buyback program, proposing it give back $50 billion more. On Sunday, Institutional Shareholder Services recommended that shareholders vote against Icahn's proposal, saying such a motion would "micromanage" how the company uses capital.

"In their recommendation, ISS points out, and we agree, that 'on the spectrum of options for allocating capital, the board appears to have been sluggish only in returning excess cash to shareholders,' and even though the company has in place 'one of the largest buybacks in history,' we agree with ISS that this effort seems 'like bailing with a leaky bucket' when 'given the scale of the company's cash reserves,'" Icahn's letter reads.

Apple has repurchased $14 billion of its stock in the two weeks since it reported first-quarter financial results and a second-quarter revenue outlook that did not satisfy investors.

In late January, Icahn said that he had bought another half-billion dollars of Apple stock, boosting the value of stake in the company to more than $4 billion.