LONDON - United States-based aluminium producer Alcoa wrote to the London Metal Exchange (LME) three times in September and October, asking for a boycott of Russian metal and greater disclosure on how much was in the LME system, the company said.

In the letters, seen by Reuters, Alcoa expressed concerns that large amounts of Russian aluminium flowing into LME-registered warehouses could distort the exchange's aluminium contract by making it reflect the price of unwanted material.

While Russia has escaped official sanctions on its aluminium, copper, and nickel of the kind imposed on some sectors following its invasion of Ukraine, some Western companies have stopped accepting Russian metal.

Alcoa is one of several US and European metals producers that have lobbied for the LME and Western governments to restrict trade in it. Some metals consumers have argued against this, saying restrictions would harm them while benefiting non-Russian producers.

In a letter to the LME dated September 29 and signed by chief commercial officer Kelly Thomas, Alcoa said it and most of its customers had stopped accepting Russian material.

It said that without buyers, more metal made by Russian aluminium producer Rusal could be deposited on the exchange, which functions as a market of last resort, leaving the LME with stocks that Alcoa said many companies and banks may not want to deal with.

"As we move into 2023 ... it is easy to see a scenario where well over one million metric tons per year of Rusal metal could be put on warrant," it said.

"The LME aluminium contract will be distorted because it will disproportionately reflect the discounted value of the Rusal brand."

The LME, the world's biggest metals trade venue, asked its users on Oct. 6 if they thought the exchange should ban Russian metal, setting an October 28 deadline for responses.

The exchange declined to comment on the letters. It said last week it could take action on Russian metal if it became a problem, without saying what it would do.

Rusal did not immediately respond to a request for comment, but said in late October its aluminium remained in demand, and that its order book for next year was nearly full.

Letters sent by Alcoa to the LME dated October 18 and October 27 said around 250,000 tonnes of aluminium that entered LME-registered warehouses in October could be Russian, and asked the LME to publish daily disclosures showing how much Russian metal was in its system.

It said it had not received a response to its request.

"Alcoa urges the LME to immediately delist all Russian brands, regardless of the production date," the company said in its October 27 letter, which was a response to the LME's request for opinions from the market.

Alcoa has also lobbied the US government to impose restrictions on Russian aluminium, something sources have said the government is considering.