Mr Pacelle will urge the company to commit to a definite time frame to phase out the confinement of sows in gestation crates - tiny cages so small that the breeding pigs cannot even turn around for essentially their entire lives.

Carl Icahn has agreed to serve as an advisor in Mr Pacelle’s efforts to join the board.

“It’s certainly unusual for a lifelong animal advocate to run for the board of the second-biggest meat company in the world,” said Mr Pacelle, who has been CEO of The HSUS for more than eight years.

“Nonetheless, it is imperative that a voice on Tyson’s board speak for the company’s many customers, partners, and investors who are demanding the end of gestation crates and more humane treatment of animals.”

A spokesman for Tyson said: "We’re not surprised Wayne Pacelle wants to sit on our board. We’re handling the nomination according to the law and our company’s by-laws.

"We’re committed to humane animal treatment and expect the same from the independent family farmers who supply us with chickens, hogs and cattle."

Mr Pacelle decided to run for Tyson’s board to encourage management there to take certain critical steps to improve the treatment of animals in its supply chain, and not fall behind its major competitors.

The HSUS said its primary focus has been for the company to join the scores of other companies who have committed to end the use of gestation crates, including the nation’s top pig producer and Tyson’s main competitor in this space, Smithfield Foods, which set a 2017 timeframe to complete its transition to group housing systems for its company-owned facilities. Hormel Foods also announced the same policy, and Cargill has been at least 50 percent gestation crate-free for five years now.

Mr Icahn said: “When Wayne Pacelle reached out to me as a long-time supporter of The Humane Society to advise HSUS on the possibility of seeking a board position at Tyson, I told Wayne that given the existence of A/B (low vote/high vote) stock at Tyson, it would be extremely difficult to elect him as a director through a proxy fight.

"However, I firmly believe that the position of HSUS regarding gestation crates is the right one. Eliminating those crates will both prevent cruelty to animals, and will improve Tyson’s business prospects by putting the company on an equal competitive footing with the bulk of the industry that is already rejecting gestation crates.

"Further, in my experience, corporate governance and transparency at companies with A/B stock is often poor and those companies in particular benefit from the sunshine of shareholder examinations as permitted under Section 220 of Delaware’s corporate laws, which may be useful in this situation and which HSUS intends to seek,” he said.

Mr Icahn added: “A fresh voice on the Tyson board would be good for the company, and I am hopeful that enough shareholders will be receptive to the campaign to put Wayne Mr Pacelle on the board so that either he will be elected, or that Tyson will reach the right conclusion and put him on the board without the cost and inconvenience of a proxy fight.”