CBS Corp. on Monday sued to stop controlling stockholder Shari Redstone from pursuing a merger with Viacom, amid fears that she could act quickly to oust the CBS board and force a deal that CBS claims would irreparably harm the company and its investors.

The lawsuit, filed in the Delaware Court of Chancery, seeks a temporary restraining order against Redstone and her family’s National Amusements Inc. holding company ahead of a board meeting, scheduled for Thursday, where CBS directors plan to issue a dividend that would reduce Redstone’s voting power from approximately 80 percent to just 17 percent.