London-listed EN+, which is in talks with the United States to have sanctions against it eased, put forward the plan in a document prepared for a shareholder meeting on Dec. 20.

The firm controlled by sanctioned billionaire Oleg Deripaska said the move could lead to a suspension or cancellation of the listing and trading of the company's global depository receipts (GDRs).

"While the GDRs are currently traded on the LSE and are expected to remain traded on the LSE following the migration, there is no guarantee that the migration will not have an adverse impact on the trading market for the GDRs," En+ said.

EN+ proposes moving to Oktyabrsky Island in Kaliningrad, a Russian exclave bordering Poland and Lithuania. Oktyabrsky Island is one of two new regions set up this year by the Russian government that offer tax breaks.

The United States imposed sanctions on EN+ and Deripaska in April, as well as several other companies he controls, citing what it described as Russia's malign activities.

However, the sanctions have been postponed several times since then as Washington considers removing En+ from the U.S. blacklist if Deripaska drops his control over the company.

(Reporting by Katya Golubkova and Anastasia Lyrchikova; Writing by Polina Nikolskaya and Tom Balmforth; Editing by Christian Lowe and Louise Heavens)