A war of words has broken out between the leaders of Slovenia's main opposition parties. The erstwhile close allies are at loggerheads after a referendum at which three government laws which the SDS, the largest opposition party, sought to bring down, were upheld by wide margins.

The SDS and NSi parties have been slowly drifting apart for months. The former has been fighting the left-liberal government tooth and nail, while the latter has occasionally endorsed major government ideas, including a set of changes to the Constitution and, most recently, an income tax bill that largely reverses a tax reform enacted by the previous, SDS government.

The tensions escalated on 20 November, following the SDS's , when NSi leader Matej Tonin said that any vote involving SDS leader Janez Janša was bound to became "irrational and emotional". He urged a serious self-reflection on the political right.

Janša retorted that if and when the NSi actually worked for and became what it is claiming to be, the party would get at least 15% of the vote in elections and many things might be different. But as long as it "merely follows the sirens and criticises those who are still fighting in this situation", the party will be struggling below 10%.

This prompted Tonin to say that the NSi would not join a Janez Janša-led government again - having previously been a partner in three Janša-led coalitions - with the caveat that they would still work together with the SDS as the party.

Adding to the debate, Ljudmila Novak, a former president of the NSi who is now the party's representative in the European Parliament, urged Janša to step down as party leader. She said Slovenia would be "sincerely grateful" to him for such a move.

The bickering comes after what one analyst has described as "the worst year so far" for the SDS, which has long been a dominant force on the right and has led three governments since 2004. First it was defeated in a general election in April, then its candidate for president lost to a political newcomer, and then it suffered heavy losses in local elections, in particular in major cities.

But another analyst, the political scientist Tomaž Deželan, told Delo newspaper that despite the defeats the party would "continue in its style". "The referendum campaign has consolidated both the power and the modus operandi of the party. This campaign has shown there is no alternative within the party."