"The only logical step now is for the prime minister to resign," head of the Democratic Party (SDS) deputy group Jože Tanko told the press.

The view was echoed by the two smaller opposition parties, the New Slovenia (NSi) and the People's Party (SLS). All three parties had petitioned the Constitutional Court over the tax.

Tanko said that this was the first time that an act essential for implementing the budget had been annulled by the Constitutional Court, highlighting that PM Alenka Bratušek had tied a confidence motion to the 2014 budget.

The decision to tie a confidence vote to the budget was "a means for forcing the coalition partners to fall into line and agree to a solution with which they did not fully agree," he said.

He argued that with its ruling, the Constitutional Court had effectively quashed the vote of confidence. This view was also echoed by SDS leader Janez Janša in a tweet.

The NSi and SLS echoed the sentiment in statements issued after the ruling was delivered.

"[Bratušek] had pegged a vote of confidence to the passage of the budget, which is now pointless," Novak argued, regretting the government had failed to listen to any argument of the opposition against the tax.

While Novak called for the prime minister to call a new vote of confidence, SLS leader Franc Bogovič argued that the government should resign outright.

"I firmly believe that today's annulment of the law has brought the Alenka Bratušek government down," said Bogovič, whose party teamed up with small businesses in petitioning the top court against the tax.

Bogovič also believes that by quashing the law, the court has protected citizens against "the governments' brutal actions" in the area of real estate taxation.

Tanko meanwhile rejected the view expressed by Bratušek today that the government was unlucky in inheriting a bad act from 2006 on mass valuation of real estate.

It is irresponsible to blame a government from eight years ago for mistakes of today, Tanko said, adding that every government had a responsibility for assessing the situation assumed from previous cabinets.

Meanwhile, SDS deputy Andrej Šircelj would not say whether the party planned to move ahead with its own attempt to oust Bratušek if she refused to resign.

"We will wait for Bratušek and the coalition to think about the situation which they are in now," Šircelj said. He said the SDS had the option of filing an impeachment motion or an interpellation motion.

However, such motions could only succeed with a defection from the coalition required for the opposition to win a majority in the National Assembly.