Last fall, Daniel Loeb, activist investor and hedge fund manager for Third Point, declared a large stake in Sotheby’s and likened it to “an old master painting in desperate need of restoration” in a letter to its board.

In the letter, Loeb called the auction house out for having “chronically weak operating margins, a deteriorating competitive position… and lack of leadership and strategic vision at its highest levels.” With a 9.62% stake in the company, Loeb called for Sotheby’s CEO William Ruprecht to step down from his position.

SothebysHowever, Mr. Ruprecht did not step down and Sotheby’s instead adopted a one-year poison pill strategy in order to prevent Daniel Loeb and Third Point, who are the single largest shareholders, from acquiring more than ten percent of the company’s stock.

Loeb called the strategy an attempt “to maintain the status quo” and “keep all of their board seats—and the prestige and lucrative compensation package that accompanies them.” Poison pills have become an increasingly popular strategy for struggling public companies in the U.S.

In February, Sotheby’s responded to pressure from Third Point by announcing a special dividend for shareholders in March, as well as announcing that it was considering selling off its New York and London Headquarters. In March, Daniel Loeb initiated a proxy contest and called for three seats on the Sotheby’s board—a request which Sotheby’s promptly denied.

Then, on Tuesday, April 1st, Third Point sued Sotheby’s for “causing irreparable damage to Third Point and other stockholders,” calling the poison pill “an improper attempt by the directors of Sotheby’s to entrench themselves in office and to hinder Third Point’s or any other stockholder’s ability to run an effective proxy contest.”

The suit filed on Tuesday calls for a revocation of the poison pill strategy, which would allow Loeb and Third Point to initiate a proxy battle and pursue a 20% stake in the company.