Dell Inc. directors’ move to change shareholder voting rules for founder Michael Dell’s buyout bid worth as much as $24.9 billion has tainted the deal, investors challenging the offer said.

Dell earlier this month changed the rules of who could vote for the deal so that abstentions no longer count as votes against Michael Dell’s offer.

A Delaware court is expected to decide Monday how fast Carl Icahn’s legal challenge to Dell’s buyout deal will move.