Proxy advisory firm ISS said it recommends shareholders vote against activist investor Carl Icahn's share buyback proposal for Apple Inc., according to a report obtained by Reuters.

"(The Apple board) has returned the bulk of its U.S.-generated cash to shareholders via aggressive stock buybacks and dividends payouts," the ISS report said.

"In light of these good-faith efforts and its past stewardship, the board's latitude should not be constricted by a shareholder resolution that would micromanage the company's capital allocation process."

Icahn is waging a campaign to get Apple to return more cash to shareholders and has filed a resolution proposing that it give back $50 billion more through share buybacks. Apple shareholders will vote on the proposal at a Feb. 28 meeting.

Proxy advisory firm Egan-Jones also advised shareholders on Friday to vote against Icahn's plan.