(By Mike Stone and Michael Flaherty for Reuters) — Billionaire activist investor Carl Icahn is building an equity stake in Time Warner Inc, people familiar with the matter said on Monday, in a move that could lead to a major shake-up of the media conglomerate.

Icahn’s intentions when it comes to Time Warner are not yet known, the people said, asking not to be named because the matter was private. Time Warner declined to comment.

Time Warner, the owner of cable channels HBO, TNT, TBS and Cartoon Network, said in November that ratings for its key domestic entertainment networks had dropped more than expected. Its shares have fallen around 30 percent since last July.

The New York Post said on Sunday that Icahn was believed to be buying up Time Warner shares and “will take another run at the company,” citing anonymous sources.

Icahn waged an unsuccessful break-up campaign against Time Warner in 2006, when current CEO Jeffery Bewkes was the No. 2 executive at the company. In 2014, Time Warner snubbed a takeover offer from Twenty-First Century Fox Inc that valued it at $85 per share.

Time Warner shares closed at $69.66 on Monday.

The company also has other activist investors in the stock. Corvex Management, whose founder Keith Meister worked for Icahn in 2006, owns 3.7 percent of Time Warner shares as of Sept. 30, Thomson Reuters data show.

Jana Partners and Greenlight Capital each own around 4 percent of the stock, the data shows. As of Sept. 30, Icahn was not a Time Warner investor, according to the data.

(Reporting by Mike Stone and Michael Flaherty in New York; Editing by Richard Chang)