(Bloomberg) -- The London Metal Exchange banned delivery of new Russian metal following sanctions imposed by the US and UK, but left the door open for a wave of old stocks to hit the market and raise the risk of pricing dislocations.

No Russian metal produced from April 13 onwards will be eligible for delivery to the LME, which plays a central role in the global metals world as the home of benchmark prices for everything from aluminum to zinc. Russian metal produced prior to Saturday will still be accepted, as long as the parties delivering it can demonstrate to the LME’s satisfaction that the metal is not subject to the sanctions.

The LME’s response means it has stuck closely to the restrictions imposed by the US and UK, and is likely to reignite a debate that has gripped the exchange since Russia’s invasion of Ukraine. Some metal traders and producers have argued that exchange should ban all Russian material to avoid being overwhelmed by a flood of unwanted metal, which they say is depressing prices and reducing its utility as a global benchmark.

In a notice to members on Saturday, LME Chief Executive Officer Matthew Chamberlain said the exchange recognized that the sanctions may cause uncertainty, leading traders to dump old Russian stocks on the LME “as a safeguarding move.”

As such, he said, “it is possible that a relatively large supply” of Russian metal may be delivered to the exchange.

The LME acknowledged that a large share of some of its metals were underpinned by Russian metal (91% of the aluminum on the LME is Russian in origin), but said that Russian aluminum had continued to be delivered out of LME warehouses in January, February and March, indicating that “a sufficiently substantial proportion of the market is still willing to take delivery of Russian aluminium.”

The LME considered banning deliveries of Russian supplies in 2022 but ultimately decided against it, arguing that there were still enough buyers willing to take delivery of the metal. While the UK imposed some restrictions on trading in Russian metals by UK entities in December, it included an exemption allowing trade on the LME to continue.

The exchange will review requests to deliver metal produced before April 13 on a case-by-case basis, while UK members looking to withdraw old stock will also need to notify the UK Department for Business and Trade, the exchange said.

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