Keith Meister, Managing Partner and Chief Investment Officer of Corvex Management, speaks during the Sohn Investment Conference in New York City, U.S., in this file photo dated May 8, 2017. REUTERS/Brendan McDermid

(Reuters) - Corvex Management threatened a proxy battle against Energen Corp if the U.S. oil and gas producer did not agree to add the activist investor’s nominees to its board.

Corvex - already the biggest shareholder in Energen - said in a filing disclosed on Monday that it raised its stake to 10.1 percent, eclipsing a threshold that allows shareholders of Alabama-domiciled companies to call a special meeting.

Corvex said in its filing that if private discussions with the company fail to result in new board members, the hedge fund intends to call a special meeting, where shareholders will vote to expand the board to 15 members from nine, and to fill the vacancies with Corvex's nominees. (bit.ly/2vC2GcG)

The $5.5 billion fund, run by activist investor Keith Meister, has often used proxy fights to press for changes at companies. Corvex’s latest battle was nominating an entire slate of directors at Williams Companies Inc last fall, a contest the fund later dropped after the oil and gas producer added new members to its board.

In a 2014 proxy fight, Corvex was among the investors that ousted the entire board of CommonWealth REIT.

Energen, a $4.5 billion energy company whose assets are concentrated in the Permian Basin in Texas, was not immediately available for comment. The company is based in Birmingham, Alabama.

Corvex first targeted Energen on May 31, calling on it to explore a sale of the entire company. Energen announced a few weeks later that after reviewing Corvex’s proposal and other strategic alternatives, it was sticking to its own business plan. The company said it hired investment bank JPMorgan Chase & Co to advise it on the review.

Energen shares were up 0.7 percent to $49.56 in afternoon trading on Monday. The stock has fallen nearly 14 percent since Corvex’s first move in May.