The billionaire activist investor Daniel Loeb has sued Sotheby’s to force the removal of a poison pill that is preventing his hedge fund from buying more of the auction house’s shares. Loeb, Sotheby’s largest shareholder, launched an attack on the company last year to encourage reforms to the company’s leadership and operations. He also spoke critically of the board’s wasteful executive compensation and waning competitive edge.

Loeb asked a Delaware court to decide whether a board can put up barriers to protect itself from a shareholder seeking board representation. Loeb’s hedge fund, Third Point, holds 9.6% of Sotheby’s, but has been prevented from building a larger stake by the board’s defensive action last October. The one-year poison pill prevents activist investors from accumulating more than 10% of the company’s stock and would make it exorbitantly expensive for Loeb to build his power in the company.

Loeb is asking for the court to overrule the poison pill, saying that his intention is to gain seats on the board and change management policies and that at no time has Third Point had any desire to take control of Sotheby’s.