Activist investor Carl Icahn, who has been waging a bitter battle against Occidental Petroleum Corp.’s board over its $38 billion acquisition of Anadarko Petroleum, cut his holdings in the oil and gas producer by nearly a third, according to an open letter to shareholders he released Nov. 8.

Icahn has opposed the deal as “hugely overpriced” and a misplaced bet-the-company gamble on oil prices rising, and urged Occidental’s board to instead put the company on the market.

Icahn sold 10 million shares and now holds 23 million shares, valued around $900 million, he said. He had owned a $1.6 billion stake in Occidental as of May 30.

Occidental bought rival Anadarko in August for $38 billion despite investor opposition to the deal, which did not go to an Occidental shareholder vote for approval.

Occidental did not respond immediately to a request for comment.

Icahn wants to replace board members, have the company accelerate asset sales, and in court is seeking documents related to the deal.

A letter to a Delaware judge earlier this week said he wants to know, “whether the actions of the directors and management were just serious mistakes or whether they represented knowing intentional breaches of fiduciary duty similar to those seen with Enron, Worldcom and other failed companies.”