The decision to investigate the proposed demerger was set into motion by a complaint from Odey Asset Management, the report said, citing emails seen by the newspaper.

The London-based hedge fund believes a recent agreement involving Rusal's two biggest shareholders means they should not be allowed to vote, the newspaper said.

Rusal said it was not aware of any investigation by the regulator, Hong Kong Exchanges and Clearing (0388) .

"We have not to date published any information concerning voting arrangements concerning any general meetings to be held," a Rusal representative told Reuters.

Hong Kong-listed Rusal said in May that it would demerge its higher carbon assets into a separate company as part of its goal to achieve carbon neutrality by 2050 and will change its own name to AL+ as part of the process.

"Rusal would focus on reinforcing its position as a leading producer of low-carbon aluminum and the new company would concentrate on the development of the domestic market and its growth potential," the Russian metals giant said in a statement at that time.

It was expected to complete the demerger process in the second half of 2022, its largest shareholder EN+ Group said on November 1.

HKEX did not immediately respond to Reuters' request for comment.