Sotheby’s adopted a “poison pill” to ward off an unwanted takeover, two days after activist investor Daniel Loeb’s Third Point LLC announced that it raised its stake in the auctioneer and called for its chief executive to step down.

The company said the shareholder rights plan would be triggered if a person or group acquired 10 percent or more of its shares.

Third Point has raised its stake to 9.3 percent, making it Sotheby’s largest shareholder.

“Poison pills” are designed to dilute holdings of an investor should its stake exceed a given threshold.