Icahn has repeatedly urged Apple to buy back an additional $150 billion of its own stock. That request has fallen on deaf ears.
Apple announced a plan in May to return $100 billion to shareholders over three years, through a combination of stock buybacks and a quarterly dividend of $3.05 per share. Apple CEO Tim Cook rejected Icahn's plan to return more of Apple's $147 billion cash hoard to shareholders after a September dinner with Icahn that the investor described as "testy."
Icahn said he will write an "in-depth letter" on the subject soon.
He started his crusade to convince Apple to buy back more of its stock in August. Since then, Icahn has upped his stake three times, continuing to praise Apple's business and calling the stock "extremely cheap." At the same time, he has skewered the company for failing to meet his demands.
Icahn wasn't the first notable investor to push Apple for a stock buyback. In February 2013, David Einhorn of Greenlight Capital publicly slammed the company for "hoarding" billions in cash. After the company announced its buyback plan three months later, a mollified Einhorn promptly increased his Apple stake.
In a letter to investors on Wednesday, Einhorn revealed that Apple remains one of his largest stock holdings, where he is betting that the stock will increase in value.