All parliamentary party heads, Prime Minister Alenka Bratušek and President Borut Pahor are expected to attend.

It is uncertain if the National Assembly will take a vote on the constitutional changes on Thursday, as the needed two-thirds support seems to remain illusive.

A meeting of deputy group leaders held on Tuesday discussed a proposal to send the motion back to the parliamentary Constitution Commission.

However, Speaker Janko Veber said after the meeting that it was too early to say anything. He expects that the meeting of top political leaders will decide how to proceed.

If the National Assembly votes on the proposal on Thursday and rejects it, this could send a negative signal to international financial markets, warned Citizens' List (DL) head Gregor Virant, who said this would be a disaster.

The prime minister finds the existing proposal under which the fiscal rule would apply for the first time in 2015 budget too optimistic.

Meanwhile, the SDS said it has no intention of withdrawing the request for the extraordinary session. It says that including the fiscal rule in the Constitution is the only good signal Slovenia can send to the world "on which it is strongly dependent".