There’s precedent for using voting control as a retention tool, Gabelli said. In the mid-1980s, billionaire Warren Buffett, agreed to vote his shares in Capital Cities/ABC Inc. with management as long as Tom Murphy and Daniel Burke, the company’s CEO and president, remained in place.

Majority of the Minority

Moonves’s level of control is just one of many issues that will likely be considered as CBS and Viacom begin discussions over a potential merger, people familiar with the process said. National Amusements requested that the businesses create special committees of their boards to consider a deal. The Redstones said they wouldn’t participate in board deliberations on the subject.

To prove their merger is backed by smaller investors, the CBS and Viacom boards may recommend that National Amusements recuse itself from any merger vote. That would mean that only the 20 percent of the voting shares not held by the Redstones vote on the deal, a practice known as a “majority-of-the-minority” vote. This approach could give Gabelli, whose funds hold more than 10 percent of the voting shares in both companies, the deciding vote in a merger.

Gabelli was among investors whose control of voting shares brought down Cablevision Systems Corp.’s plans to go private in 2007 when the Dolan family allowed a majority of the minority to vote on that deal. To prevent Gabelli from dictating the outcome of a transaction, as a matter of perceived fairness, CBS and Viacom could allow the owners of Class B Viacom shares, which don’t have voting rights, to vote on the deal anyway.

Gabelli said he would have concerns about letting Class B shareholders vote.

“That would be very unusual,” he said. “I paid a premium to get the voting stock for my clients.”

More Fair Outcome

Majority shareholders like National Amusements don’t legally need to seek approval from minority investors for a merger. But courts in Delaware, where CBS and Viacom are incorporated, have been encouraging companies to do just that to produce a more fair outcome, according to Lawrence Hamermesh, a professor of law at Widener University’s Delaware Law School in Wilmington.

There’s no reason Gabelli couldn’t be given the deciding vote, if there aren’t any circumstances where he shouldn’t, Hamermesh said. He said he’d never heard of a situation where non-voting shareholders got the right to vote.