(Adds background, details from letter)
Sept 29 (Reuters) - Sumner Redstone's National Amusements, the majority shareholder of CBS Corp and Viacom Inc , said a merger of the two would offer substantial savings and that it would not support the acquisition of either company by a third party.
Privately held National Amusements, which owns 80 percent of the voting shares of both media companies, also said it would not support a transaction that would cause it to surrender control of either company or a combined entity.
CBS and Viacom first separated 10 years ago.
"We believe that a combination of CBS and Viacom might offer substantial synergies that would allow the combined company to respond even more aggressively and effectively to the challenges of the changing entertainment and media landscape," said the letter signed by Redstone and his daughter Shari Redstone.
The optimal deal structure would be an all-stock transaction in which holders of each company would receive shares in the combined entity of the same class as they currently hold, National Amusements said in a letter to the companies' boards.
Any transaction would require the approval of both boards. Sumner Redstone, Shari Redstone and David Andelman will not vote as directors on the deal and will not participate in deliberations, according to the letter.
Reuters reported on Wednesday that National Amusements, owned by Sumner and Shari Redstone, could contact CBS and Viacom as soon as this week to ask them to form independent board committees to discuss a potential merger. (Reporting by Anya George Tharakan in Bengaluru and Anna Driver in New York; Editing by Ted Kerr and Lisa Von Ahn)