The proposal to give the leader of the Marjan Šarec List (LMŠ), the runner-up in the 3 June election, the mandate to form the government was filed by 43 MPs of his emerging coalition last week.
Apart from the LMŠ, the five-strong centrist coalition features the Social Democrats (SD), Modern Centre Party (SMC), Pensioners' Party (DeSUS) and Alenka Bratušek Party (SAB).
The 13th Slovenian government, expectedly to be endorsed in mid-September, will be formally a minority government, but will enjoy the support of the Left with nine MPs.
Committing to a project-based cooperation, the quintet and the Left have initialled a special protocol pledging to try to reach a compromise on all government measures.
They have also identified common solutions to some other issues, such as healthcare, poverty reduction, minimum wage and pensions increases, and permanent employment.
The priorities for 2018 have also been set: rising pensions and cutting waiting times in healthcare will be their key common projects, while a new minimum wage bill will be the priority of the Left.
Under the protocol of cooperation, the Left is obliged to support the coalition in voting on the prime minister-designate, national budget, and parliament's leadership.
At tomorrow's extraordinary session, which starts at 10 AM, the MPs could also appoint a new parliamentary speaker to replace incumbent Matej Tonin of the conservative New Slovenia (NSi), and deputy speakers.
The five prospective coalition parties submitted a formal request with MP signatures to expand the parliament's agenda today, arguing Tonin was to serve only until a coalition is formed.
The quintet has already agreed to put forward SD leader Dejan Židan as speaker, and Tina Heferle (LMŠ) and Monika Gregorčič (SMC) are candidates for deputy speakers.
If appointed tomorrow, PM-designate Šarec will be due to submit a list of ministerial candidates (which requires the majority of all MPs present at the session) by 3 September at the latest, and a vote on it would follow between 11 and 14 September.
Should he fail to submit the list by then, the National Assembly could set a new period for the list to be put forward. Should he fail to do so again, Šarec would lose the mandate.
In case Šarec, the mayor of Kamnik, is not appointed prime minister-designate on Friday, parliament would be dissolved and a new election called.
However, the National Assembly could also decide to appoint a new prime minister-designate in 48 hours in what would be a third attempt to elect a prime minister-designate after this year's snap election.
Indeed, Tonin said tomorrow's agenda also featured a "potential" vote on a prime minister-designate in third round, which is also the last one under Slovenian law.
The first attempt failed when Janez Janša of the Democrats (SDS), which won most of the vote in the election, renounced the mandate when most of the parties declined to work with him due to what they perceived as extremist rhetoric, and Šarec was still amid talks to secure support.