PARIS (Reuters) -U.S. investment firm American Industrial Partners plans to sell or list on the stock market Aluminium Dunkerque, France's largest aluminium plant, a union official said on Friday.

The local management informed workers representatives of AIP's plan, Johan Vlietinck, a representative of the CGT union at the site, told Reuters.

Bloomberg News had reported earlier that AIP was considering a sale or listing for Aluminium Dunkerque, which it acquired four years ago following a debt default by GFG Alliance, owned by commodities tycoon Sanjeev Gupta.

A spokesperson for AIP in France said the investment fund was not denying the press reports but would not comment further.

Aluminium Dunkerque could not be immediately reached for comment.

Unions had anticipated a possible sale after Aluminium Dunkerque signed a 10-year power contract with utility EDF in May, providing long-term cost visibility for the energy-intensive business, Vlietinck said.

Aluminium Dunkerque, which produces around 300,000 metric tons of raw aluminium per year, has an annual power consumption roughly equivalent to that of Marseille, France's second-largest city. It generates annual turnover of more than 800 million euros ($921.4 million), according to its website.

No offers for the business have been communicated to worker representatives, Vlietinck said, adding that the CGT union would like the French state to invest as part of a consortium.

France's economy ministry did not immediately respond to a request for comment.

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