Harbinger Capital Partners, which has launched activist campaigns against several major media companies, may be on the verge of another. The activist hedge fund manager has taken a big stake in the U.S.’s fourth-largest cable television operator, Cablevision Systems.

Harbinger disclosed a 4.9% stake in Bethpage, N.Y.-based Cablevision, and owns call options that could increase its stake over 5%, at which point it would have to declare its intentions. It also said it may increase its stake even further.

The Cablevision shares, purchased in six recent transactions, make Harbinger the fifth-largest in the company.

The prospect of a battle with Harbinger may explain Cablevision’s recent unusual behavior. The company held meetings with its largest investors for the first time in years, and declared a quarterly dividend on Friday. Earlier this month, CEO James Dolan, who also runs the New York Knicks basketball team, said Cablevision was investigating ways to boost shareholder value.