RWE, the German energy company, has launched arbitration proceedings over undelivered volumes of gas against Russian state energy giant Gazprom, according to a report in the Handelsblatt newspaper Monday, quoting RWE’s spokesman.

Although RWE was not highly reliant on the Russian deliveries, with Gazprom only to cover 15 terrawatt hours (TWh) by next year, and the missing deliveries only amounted to 4TWh, experts say RWE may pursue damages in the hundreds of millions of dollars for the missing deliveries.

Martin Tessier, an analyst from Stifel Research, said that, “in the event of a full cut of supply, we calculate that the replacement of the remaining 4 TWh could cost at least an additional €400 million ($422 million).”

The RWE spokesman did not expound on the legal process to the newspaper. However the legal action will follow closely on Uniper, Germany’s largest gas importer, suing Gazprom for billions of euros over the reduced supplies it received as the Nord Stream pipeline flows gradually reduced to zero.

Soon to be nationalized, Uniper claims that the cost of replacing the lost Russian gas flows has been roughly €11.6 billion ($12 billion) and that number will only grow between now and the end of 2024.

Gazprom has confirmed that Uniper has initiated arbitration proceedings as well, however it denies any violation of any contracts, and rejects the legitimacy of any claims over damages. So far Gazprom has not commented on RWE’s action.

Russia has claimed it was not able to maintain the flows through the Nord Stream 1 pipeline, due to its inability to perform maintenance, which was a result of the western sanctions on Moscow following the military conflict in Ukraine. The Nord Stream 1, as well as one leg of the Nord Stream 2 pipelines were blown up subsequently,

Moscow has offered to resume gas flows through the remaining leg of the Nord Stream 2 pipeline, however Germany has refused to approve the line for service.