Answering a question during a panel at an event honoring Buffett's 50 years at Berkshire, Ackman says, as quoted by The Wall Street Journal, that he has a "problem" with holding Coke stock, accusing the company of causing "enormous damage to society" by displacing the "water that children and adults consume with sugar water."
"Coca-Cola has probably done more to create obesity and diabetes on a global basis than any other company in the world," he told the gathering.
Coca-Cola called the comments "irresponsible" and said they "do not recognize the current breadth of our business."
It's not total war between Buffett and the value investor who's been labeled a "Baby Buffett" by Forbes magazine.
The Journal reports that Ackman called Buffett deeply ethical and deserving of admiration and respect. Ackman even noted that Buffett's own health doesn't appear to have been hurt by his habit of drinking multiple Cherry Cokes a day.
Ackman's jab follows negative comments by Charlie Munger, Buffett's business partner, about Valeant Pharmaceuticals, one of Ackman's biggest holdings.
Munger called Valeant "deeply immoral" and accused it of price gouging with its steep increases for what it charges for some drugs. The stock has also been sliding amid accusations by short sellers that it had an improper relationship with a pharmacy that sold its products.
Ackman has defended Valeant and called the stock a bargain as its price has dropped.