As he had promised via recent Twitter messages, billionaire investor Carl Icahn issued an open letter to shareholders of Apple and once again urged them to support his proposal for a new $50 billion buyback. Icahn also said that he increased his stake in Apple by another $500 million, bringing his total holdings in the iPhone maker to $3.6 billion.

He said that Apple Apple is undervalued, and urged for an even largest share repurchase than the "conservative" one Apple is currently running.

"..we believe that the combination of the company's [Apple] unprecedentedly enormous net cash balance, robust annual earnings, and tremendous borrowing capacity provide more than enough excess liquidity to afford both the use of cash for any necessary ongoing business-related investments in addition to the cash used for the increased share repurchases proposed," he said.

".. by choosing not to increase the size of the repurchase program, the directors are actually performing a great disservice to the owners, especially smaller shareholders who may not be in a position to buy more stock themselves," Icahn added.

"..we believe Apple is undervalued in order to express how ridiculous it seems to us for Apple to horde so much cash rather than repurchase stock (and thereby use that cash to make a larger investment in itself for the benefit of all of the company's shareholders)."