Prime Minister Arseniy Yatsenyuk said Ukraine's government and state gas company, Naftogaz, would begin legal proceedings against Gazprom if it did not agree to arbitration within 30 days.
"Today (Monday) we sent a pre-arbitration note" to Gazprom he said in a televised address.
"We are waiting for a Gazprom answer... Unless we reach an agreement within 30 days, we will move from pre-arbitration phase to a legal case," he said.
Gazprom late last month said it was seeking $485.50 per 1,000 cubic metres, after scrapping a discount applied to Ukraine when it was in Russia's orbit.
Kiev wants the matter to be settled by the international arbitration section of Stockholm's chamber of commerce.
However, it is far from clear that Moscow, which said this year it did not recognise the Swedish arbitration body's jurisdiction, will agree to that path.