The motion, which was tabled by a group of 31 MPs headed by Bojan Kontic of the ruling Social Democrats (SD), was passed at first reading last week with a majority of only 31 votes in the 90-strong Assembly.
This time the vote was 7 to 5 against. Kontic called the decision "irresponsible", noting that the EUR 1.3bn investment in TES6 was ongoing and that contracts had been signed.
Given today's vote, the plenary will only be acquainted with the committee's decision as it meets for an extraordinary session scheduled on Tuesday.
Kontic said the proponents of the motion from the ranks of the opposition Democrats (SDS) had "pulled out" and were probably counting on coming to power after the December general election.
The business daily Finance reported that the SDS had had a change of heart and that the former Economy Minister Andrej Vizjak believed it would be better to wait with the bill until after the election.
Kontic hopes the European Investment Bank (EIB) and the European Bank for Reconstruction and Development (EBRD) will wait for a new government to be formed, and withdraw only then if it turns out there will be no state guarantee.
Zares, who have been the most vocal opponents of the TES6 project, welcomed the rejection of the bill as a "big blow to the energy lobby and to the grand coalition", as Zares leader Gregor Golobic said in his Tweet.
In today's debate, SocDem MPs Luka Juri and Matevz Frangez and Alojzij Potocnik of Zares opposed the bill citing concerns about the economic efficiency and environmental acceptability of the TES6 project.
Radovan Zerjav of the opposition People's Party (SLS) announced his abstention, arguing that the time ahead of the election was inappropriate to decide on such projects. He also maintained that the worst thing would be to halt the project at this stage.
Speaking on behalf of the largest opposition party, Zvonko Cernac explained that the Democrats (SDS) were not unanimous on the issue, so they would vote according to their conscience.
He said decision was no longer about the project, but about whether it would be less or more expensive. He mentioned the threat of a referendum against the motion, arguing that a suspension of the project would cause major damage.
The boss of Sostanj power plant TES Simon Tot told MPs that halting the project would cause costs amounting to EUR 1.8bn, while the taxpayer would not have contribute a single euro if TES6 is completed.
Each month of delay on the project means EUR 6m in extra costs, said Matjaz Janezic, general manager of energy utility HSE, the owner of TES.
HSE and TES also said in a press release that in the worst case scenario banks could pull out of the deal and withdraw loans that had already been used.
"The result of the vote benefits neither TES nor Slovenia as a whole; it all seems that the burden of pre-election battle will be transferred to the Slovenian taxpayers through the strategical energy project at the end of the day," the companies wrote in a press release.
The project was also backed by Marko Golob of the Capital Assets Management Agency (AUKN), who said that on inspecting the documentation, the agency established allegations of opaque management of the project were unfounded.
The EIB and the EBRD decided to finance the project based on studies they had commissioned themselves and which found TES and its supplier, Velenje coalmine, were "top-notch organisations in their field", Golob said.