Activist investor Ancora Holdings is preparing to wage a proxy battle at U.S. Steel and wants the company to drop its merger agreement with Japan's Nippon Steel, the Wall Street Journal reported on Sunday, citing sources.

Ancora also intends to rally shareholders around a plan to oust U.S. Steel's top boss David Burritt, the report said.

The activist investor is not interested in pursuing a sale of the American steelmaker to another party, the WSJ reported, adding that Ancora has nominated nine director candidates to the company's 12-person board, including Stelco's former chief Alan Kestenbaum.

Ancora, U.S. Steel and Nippon Steel did not immediately respond to Reuters' request for a comment outside regular business hours.

Earlier this month, former U.S. President Joe Biden blocked Nippon Steel's $14.9 billion deal for U.S Steel, and delayed an order until June for Nippon to abandon the bid.

The companies have sued the Biden administration for blocking the acquisition of U.S. Steel by the Japanese company.