MOSCOW (Reuters) - Russian gas giant Gazprom said on Wednesday it has lodged a claim against German energy group Uniper under an international arbitration act in relation to gas prices for 2018.

In the past, Gazprom and Germany’s E.ON, from which Uniper was divested as a separate legal entity two years ago, had a history of arbitration proceedings over gas prices.

“The application for an arbitration in order to resolve a contractual dispute is a standard practice foreseen in such contracts,” a Gazprom spokesman said, adding that Gazprom wants the contract revision for gas prices starting from Feb. 1.

Uniper said it was studying the matter, without elaborating.

Uniper is Gazprom’s key partner in Germany, the biggest consumer of Russian gas. Gazprom has four contracts with the company until 2035.