KYIV, May 27 – Naftogaz Ukrayiny has started a pre-arbitration procedure due to Gazprom's failure to comply with a "pump or pay" condition under a contract for organizing natural gas transit, Naftogaz head Yuriy Vitrenko has said.

"We have already started the pre-arbitration procedure. We are preparing appropriate appeals to Gazprom with lawyers. The reason is that they pay less than they should pay under the contract. They have no justification for this – our contract is pump or pay," he said in an interview with Interfax-Ukraine.