The decision comes after the Virant List opted against a coalition with Janković's Positive (PS) Slovenia on Monday, announcing it would not back him for PM-designate, while the Social Democrats (SD) have promised their support.

The PS, SD and Desus only have 44 seats between them in the 90-strong National Assembly, which means that Janković does not enjoy sufficient support to get appointed PM-designate tomorrow.

The remaining parties had already indicated earlier that they will not back Janković, while the two MPs representing the Italian and Hungarian minorities say they will not be the deciding factor.

DeSUS leader Karl Erjavec came out of the meeting of the party's executive council by expressing satisfaction with the coalition agreement drawn up by the PS. He said DeSUS had managed to include everything it was interest in in the document.

Specifying, he said that they had agreed not to subject pensions to a potential austerity act in 2013, and a compromise for a pension reform to index pensions 60% to pay growth and 40% to growth in the cost of living.

The prospective coalition partners also pledged to prevent abuse of early retirement. "Some people retire early, even though they are fit to continue working, thus placing unnecessary burden on the pension purse."

Erjavec added that DeSUS had also managed to include in the coalition agreement its proposal for a fourth income tax bracket to raise the burden on top earners, and for subsidizing internship for understaffed jobs.

Erjavec said DeSUS had negotiated two ministerial posts, but since the Virant List had announced it would not join the Janković-led coalition, the distribution of ministerial posts would be different now.

The party decided to back Janković for PM-designate "even though we know he doesn't have the necessary votes at the moment", Erjavec said, adding that Janković had indicated today that "he has these votes".

The executive committee also discussed the possibility that Janković fails to get a sufficient vote, giving the party president and negotiating team the mandate to enter talks with another potential PM-designate.

The potential centre-right coalition of the Democrats (SDS), Peoples' Party (SLS), New Slovenia (NSi) and the VL also has 44 seats in parliament, which means they would need DeSUS to build a majority government.