While Bratušek has already announced her plan to stand for re-election, the public is eagerly awaiting Janković's decision after he said he would challenge her at the party congress last year, but has been rather vague about it lately.

The clash between Bratušek and Janković could topple the government, which was formed in March 2013 after prospective coalition partners set Janković's withdrawal from the top of PS as a condition to enter coalition with the PS.

The prospective coalition parties had refused to work with Janković after the anti-corruption commission established in January 2013 that he could not account for around EUR 2m in assets.

In this way he was forced to step aside, which enabled Bratušek to form a government when the Janez Janša government was voted out of office after the same commission established that Janša could not account for some of his assets.

Last week, Karl Erjavec of the coalition Pensioners' Party (DeSUS) mentioned a third possibility to prevent a political crisis if Bratušek fails to get re-elected.

He believes Bratušek and those PS MPs who support her could defect from PS and form their own party, so she could remain prime minister.

This is however unlikely as it is not clear how many MPs actually support Bratušek.

Some even hold it against her that she has announced a vote of confidence in parliament merely to "discipline" her own deputy group, some of whose members support Janković.

The leader of the PS deputy group Jani Möderndorfer has denied speculation that Bratušek would seek the vote of confidence to force PS MPs to stand behind her.

He said the vote was meant to put an end to speculation whether it was right for Bratušek to continue to be prime minister.

The date of the confidence vote is yet to be revealed, but pundits speculate it would be held before the party congress, so that by surviving it, the prime minister would strengthen her position against Janković at the congress.

The new party president will be elected in secret ballot.

With the exception of those who join the PS after 10 April, when the date of the congress was set, all party members attending the congress will have the right to vote.

The deadline for Bratušek and Janković to speak out their minds about the party presidency was set last week by the PS executive committee, which set the date of the congress.