BRUSSELS — European Union authorities on Tuesday stepped up efforts to reduce reliance on Russian natural gas as the two sides face off over a litany of geopolitical disputes, from the conflict in Ukraine to the civil war in Syria.

The centerpiece of the proposals, presented by the European Commission, the bloc’s executive agency, is a plan to vet energy contracts with countries outside the union like Russia so that member states can compare conditions and look elsewhere for better deals.

Energy is a highly sensitive issue for Europe and Russia. The European Union relies on the Russian energy giant Gazprom for about a third of its supplies. Moscow, in turn, earns significant revenue from selling gas to Europe.

The commission’s priority is to prevent a repeat of the so-called gas wars of 2006 and 2009. Back then, Gazprom stopped shipping fuel through Ukraine, choking off supplies westward and leaving citizens in member states like Bulgaria shivering in the midwinter cold.