American Industrial Partners logo is shown in this illustration taken August 21, 2025. REUTERS/Dado Ruvic/Illustration
The storage of aluminium ingots and plates at the aluminum smelter Aluminium Dunkerque in Loon-Plage near Dunkirk, France, September 22, 2022. REUTERS/Pascal Rossignol

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 did not respond to a request 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, located next to the northern French port of Dunkirk, produces around 300,000 metric tons of raw aluminium per year. It 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 workers' representatives, Vlietinck said.

Bloomberg cited sources saying there had been non-binding offers from companies including Rio Tinto <RIO.L>, Glencore and Metlen Energy & Metals. The three companies mentioned all declined to comment.

The CGT is opposed to any potential return of mining group Rio Tinto, which it considers to have underinvested during its ownership of the site before selling it to GFG Alliance, Vlietinck said.

The union would like the French state to invest as part of a consortium, he added. France's economy ministry did not immediately respond to a request for comment. ($1 = 0.8682 euros)

(Reporting by Gus Trompiz, editing by Inti Landauro, Kirsten Donovan and Alex Richardson)