In a tweet Wednesday, Icahn wrote: "Gave $AAPL notice we'll be making a precatory proposal to call for vote to increase buyback program, although not at $150 billion level."
A "precatory" proposal is one that is considered an advisory measure, but not necessarily legally binding. Apple's annual shareholder meeting typically takes place in February.
Icahn revealed his large stake in Apple this summer and said he would begin pressing the company to increase the size of the stock buyback. Although the company had announced a record stock buyback and dividend program worth over $100 billion earlier this year, Icahn argued the company was making so much cash that it needed to raise the amount even more.
Apple has acknowledged the issue, and typically says it continues to review how it manages its cash and the size of its stock buyback and dividend programs.