According to a written statement issued by four of them, the group left the party over the selection of the candidates for the mayor and city councillors.

They argue that the local leadership violated the party's internal rules by picking the candidates without all active local membership participating in the decision.

SMC party leader Miro Cerar regretted the resignations, but downplayed them as part and parcel of the formation process in any new party, arguing that tensions were normal at this stage.

The group that left suggested some the SMC MPs from the area and the local party officials formed the list of candidates based on their private interests and familial and crony ties.

But SMC candidate for Maribor mayor Anton Kranjc told the STA that he had not been notified of the resignations, which he said came at a very inauspicious time and could harm his bid.

He said he suspected the timing was deliberate as there had been no protests concerning the candidates in the past two weeks, but he admitted some might have been unhappy about not being fielded.

Speaking for the disgruntled group, Robert Šitum said they opted for the move two days ahead of the vote because they had been waiting for a response from the leadership of the party, which they did not get.

He also rejected the allegation that they were offended because they were not placed on the list of candidates for the city council.

Head of the local chapter Andrej Špenga said that the party had not received a single resignation yet, suggesting that those who left entered the party in ill faith.

He said that some had wanted to get into the city council through the SMC, although they had been in contact with other parties all the time.

The party is projected to win the vote for the Maribor city council, while its mayoral candidate is projected to come second or third behind the incumbent mayor.

"I regret the event but I want to underline that I'm firmly behind our list and the mayoral candidate in Maribor," PM Cerar was cited as saying by the web news site rtvslo.si.

He promised an analysis of the resignations in Maribor for after the election, but said that it was common for people to join a new party with some expectations, but were then put off by failing to achieve that.

The row comes after the SMC was left by MP Bojan Dobovšek, one of the founding members, and its member Jure Leben was resigned as state secretary over the allegation that he misrepresented his academic title.

The development fuelled speculation about a rift in the SMC, which party leader Miro Cerar refuted as "tragicomic" with party MPs rushing to deny rumours about internal tensions.