President and Chief Executive Officer of CBS Corporation Leslie Moonves poses for a portrait in his office in Studio City, California February 1, 2016. CBS Corp said on Wednesday that media mogul Sumner Redstone had resigned as executive chairman, a move that comes amid heightened questions about the 92-year-old billionaire's physical and mental health. CBS said Redstone would be replaced by Leslie Moonves, its president and chief executive since 2006. REUTERS/Mario Anzuoni TPX IMAGES OF THE DAY - RTX25CAX

(Reuters) - CBS Corp Chief Executive Leslie Moonves should get five years without interference from Sumner Redstone’s family if the media company is merged with Viacom Inc, investor Mario Gabelli told CNBC on Tuesday.

The Redstone family’s National Amusements Inc holds 80 percent of the voting shares in CBS and Viacom, and has urged the two companies to consider a merger.

“Give him five years,” said Gabelli, who is the second-largest owner of voting shares of both Viacom and CBS after the Redstone family.

“Say I will stay off your case,” he said, referring to Shari Redstone, daughter of the media magnate, who has been taking a more active role in her father’s business interests in the past year.

Both CBS and Viacom have formed independent board committees to consider a merger at the behest of National Amusements, but it is not clear if terms can be reached. National Amusements has said it will not support any other transaction, nor will it give up its controlling interest in the companies.

Viacom, which owns Comedy Central, MTV and film studio Paramount, has been struggling with declining ratings and ad revenue. Moonves wants autonomy to run the combined company if a merger takes places, sources have told Reuters.

A spokeswoman for Shari Redstone declined to comment.