Sumner Redstone, who spent three decades building mass media giant Viacom Inc., has made a move to dramatically overhaul the Viacom board, the latest twist in the increasing turmoil surrounding his $40 billion empire. The move immediately triggered a legal battle over control of the corporation, as Frederic V. Salerno, one of five directors whose ouster is sought, filed suit in Delaware to invalidate the dismissals.

The ouster effort follows months of drama involving Mr. Redstone’s daughter, Viacom Vice Chair Shari Redstone, as well as longtime associates and even past romantic companions. The move reflects an intensification of the ongoing fight for control of the empire built by Mr. Redstone, now 93 and in declining health.

Mr. Salerno, Viacom’s lead independent director, said in a statement that Shari Redstone is responsible for the board overhaul move.

National Amusements, the holding company through which Mr. Redstone controls Viacom, did not reveal the reasons for removing the board members. However, Mr. Redstone has hinted at frustration after a nearly 40% slide in its stock over the past year.

In addition, two top Viacom executives removed from their duties last month have sued in Massachusetts court to challenge their removals. They argue that Ms. Redstone is orchestrating the changes and is taking advantage of her father’s declining mental competency to implement changes she wants.

David Margules, a partner at Ballard Spahr LLP with experience litigating cases in the Delaware court, said the Viacom directors would have a tough argument. "The proponents of the status quo are going to have to show the board takeover poses a threat to the corporate enterprise."

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