CBS on Wednesday defended a board vote that sharply reduced the voting power of Shari Redstone, its controlling stockholder, filing an amended complaint that her bid to block the move was “inequitable and invalid” and arguing that it acted to preserve the discretion of independent directors.

In the battle for control of the company, CBS Corp. directors moved quickly last week amid fears that she would use her influence to oust directors and force a merger with Viacom Inc. At a special board meeting on May 17, CBS directors approved a stock dividend that diluted Redstone’s voting power from about 80 percent to 20 percent.