The power struggle has put at stake the future of the $40 billion broadcast entertainment business, which owns hit names like MTV, Nickelodeon and Comedy Central and Paramount Pictures.
Billionaire Sumner Redstone has sacked two longtime allies at the trust controlling Viacom and CBS. The move is seen as an attempt by Redstone to gain the control of Viacom.
"We will contest the purported removal if it comes, because we see that as our responsibility to the non-control shareholders of Viacom who own 90 percent of the equity of the company - and to the legacy of a man we greatly admire and consider a dear friend," lead independent director Frederic Salerno wrote in a letter to shareholders.
"We can do no less than try to make sure that the fates of Viacom, its majority equity holders and Sumner's legacy are ably represented on their behalf and impartially decided by the courts," he added. The letter was made public Monday.
Salerno said he and governance and nominating committee chair Bill Schwartz tried their best to meet Redstone but in vain. "We feel the responsibility to challenge in court what we honestly believe would be legally flawed removals," he said, writing on behalf of six Viacom board members.
"That is especially so because the flaw we see would be the inexplicable assertion that Sumner was acting of his own free will and with the mental competency to do so," he added.