Pahor will be challenged by three other candidates, but only two stand serious chance: Igor Lukšič and Patrick Vlačič, both of which served as ministers in his government in the 2008-2011 term.

Heading the party since 1997, Pahor is largely credited with lifting the former reformed Communist party from the doldrums and eventually taking it to victory in the 2008 general election.

He did not get to complete his term as prime minister, but he still managed to get the party fairly well out of the December 2011 snap election with 10.5% of the vote.

Yet steadily growing grievances against him within the party culminated this year as his views often clashed with those of the other senior members, who accused him of being too close to the policies of PM Janez Janša.