My colleague Andrew Bary this morning reports this morning that one of Comcast’s (CMCSA) largest institutional shareholders, Chieftain Capital, is asking the company to axe CEO Brian Roberts, to return more cash to holders in the form of buybacks or dividends and to scrap the company’s dual-class voting structure.

Andrew notes that in a Jan. 14 letter to the company, Chieftain called the Roberts’ stewardship of Comcast a “Comcastrophe,” notes that the stock is no higher than it was in late 1998, and asserts that “it is time for change.” Chieftain owns 60.5 million shares of Comcast stock on behalf of clients, about 2% of the company.

As Andrew points out, Comcast’s shares are down nearly 40% in the past year and off by 25% since the company gave disappointing 2007 financial guidance in the fall.

Comcast today is down 49 cents, or 2.7%, at $17.69.

Update: Pali Research has posted a copy of Chieftain’s letter to Comcast’s board.