Bulgaria’s likely next prime minister said on Wednesday the country will push ahead with a Russian gas pipeline only if it complies with European Union laws, signaling a more defiant posture than the outgoing Socialists.

The conservative Boyko Borisov, who was prime minister between 2009 and 2013, also told the Reuters news agency he would scrap a tender awarded to a consortium led by the Russian construction company Stroytransgaz for the Bulgarian leg of the South Stream pipeline. The firm’s owner is on a list of Western sanctions targets imposed after Russia annexed Ukraine’s Crimean Peninsula in March.

Borisov is expected to return to power after the ruling Socialist Party performed poorly in May’s European Parliament elections.

But Bulgaria’s uncertain participation in South Stream has also frayed relations within the ruling coalition.

Earlier this month, incumbent prime minister Plamen Oresharski said Bulgaria was suspending work on South Stream despite earlier championing the project. His announcement came after the European Commission had put the approval process for the Russian pipeline on hold in the wake of the Crimea annexation, claiming the project did not comply with its regulations on ownership and pipeline access. Yet Oresharski’s energy minister later contradicted him, saying the decision to back South Stream was “irreversible.”

Stoking the row inside the coalition between Oresharski’s Socialist Party and the Turkish liberals was the European Union’s withholding of tens of millions of euros in regional development funds, meant to pressure the Bulgarians into delaying South Stream’s construction.

Planned for completion in 2018, South Stream would bypass Ukraine which currently pipes roughly half of Russia’s gas exports to Europe. The submarine part of the pipeline will pump Russian gas to Bulgaria’s Black Sea port of Varna before it extends overland through Serbia, Hungary and Slovenia.

Bulgaria is almost totally dependent on gas supplies from Russia. Russia’s Lukoil also runs its only oil refinery which supplies over 60 percent of the country’s refined fuel.

In May, Russia circumvented the European Commission’s boycott by signing a bilateral agreement with Austria where the pipeline is designed to terminate. However, if Bulgaria pulls out, it would probably still be unable to complete the pipeline.