Billionaire investor Carl Icahn is happy enough with Apple to keep buying shares in bulk, but he does want the tech company to make some changes, and he’s breaching the topic on Twitter.

Icahn and his company, Icahn Capital Management, have been pushing management to buyback Apple shares since August 2013, when he said the company was “extremely undervalued.” He also took the opportunity to urge Apple CEO Tim Cook to offer larger stock buybacks, in which Apple would reacquire its own stocks.

Now, nearly half a year later, it seems Icahn is still waiting for that to happen. He reiterated his position in a series of tweets this morning:

Since tweeting about our large position in $AAPL on Aug 13, when the stock was 468 per share, we’ve kept buying shares of this ‘no brainer.’

— Carl Icahn (@Carl_C_Icahn) January 22, 2014

 

Having purchased $500 million more $AAPL shares in the last two weeks, our investment has crossed the $3 billion mark yesterday.

— Carl Icahn (@Carl_C_Icahn) January 22, 2014

 

We feel $APPL board is doing great disservice to shareholders by not having markedly increased its buyback. In-depth letter to follow soon.

— Carl Icahn (@Carl_C_Icahn) January 22, 2014

Cook has shown previously that he’s open to suggestions from major investors, and Cook has even met with Icahn in the past. Now the ball’s in his court once again to keep Icahn and his followers happy.