The regulation on CO2 standards will be put to a final vote on Tuesday during a meeting of energy ministers.
Italy and Poland have opposed a deal struck over the weekend between Brussels and Berlin that would exempt vehicles than run exclusively on e-fuels from a 2035 ban on the combustion engine.
Bulgaria and Romania abstained during a discussion at the ambassadors level on Monday morning, according to five officials from different countries who spoke to Euronews on condition of anonymity.
But their joint resistance falls short of the necessary votes to halt the legislative approval, widely expected to be completed on Tuesday.
The Brussels-Berlin deal relates to an agreed-upon regulation that is set to impose a 100% reduction in CO2 emissions on new sales of cars and vans sold across the European Union as of 2035.
The law was designed by the European Commission as "technologically neutral," but given that CO2 emissions will be measured at the exhaust pipeline, it will effectively outlaw sales of petrol and diesel cars after the cut-off date.
By contrast, sales of electric vehicles will be allowed.
Earlier this month, Germany, a country that hosts a world-class automotive industry, mounted a surprising opposition campaign and blocked the final green light of the regulation, which had been meticulously negotiated between member states and the European Parliament.
The German hold-out shocked officials and diplomats, who saw it as a betrayal of the long-standing rules of procedure. Numerous MEPs and several member states, such as France, Spain and the Netherlands, have said the text was closed and would not be reopened.
The deadlock prompted a rare intervention by European Parliament President Roberta Metsola, calling for the respect of "legislative predictability."
"We cannot go back on deals because this is ultimately about trust between co-legislators and the credibility of the legislative process," Metsola said last week.
In a bid to break the impasse, European Commission Executive Vice-President Frans Timmermans, who is in charge of the European Green Deal, engaged in direct talks with Volker Wissing, Germany's federal minister for digital and transport.
Wissing, a liberal politician from the pro-business FDP party, personally pushed for a tailor-made exemption for e-fuels, an emerging technology that combines hydrogen and carbon dioxide to produce synthetic fuels.
E-fuels can be poured into existing cars, therefore ensuring the survival of the combustion engine after the 2035 deadline. Although they can theoretically be climate-neutral, detractors argue e-fuels are energy inefficient and have limited commercial viability.
The intense negotiations between Brussels and Berlin bore fruit over the weekend when the two sides found a compromise.
The deal has not yet been made public.
"Europe remains technology-neutral. Vehicles with combustion engines can also be newly registered after 2035 if they only use CO2-neutral fuels," Wissing tweeted on Saturday, celebrating the news.
The regulation, together with the e-fuels exemption, was discussed by ambassadors on Monday morning with the goal of including it on the agenda of Tuesday's meeting of energy ministers.
It was during this exchange of views that Italy and Poland raised objections.
Italy had previously called for an exemption for biofuels, which emit fewer CO2 emissions than oil-based fuels but have been criticised for their land use.
"Forcing electrification may, on the contrary, entail the risk of non-acceptance by the market, which could harm car and van producers. It would also prevent the technological development of hybrid engines with a very low environmental impact," Italy wrote in the meeting's minutes, seen by Euronews.
"Any additional costs resulting from the new burdens should be borne by manufacturers and not passed on to citizens," Poland said.
Bulgaria and Romania expressed points of view interpreted as an abstention, diplomats said, while Finland regretted the omission of biomethane, a gas-based type of fuel.
But with Germany on board, the remaining reluctant countries were unable to form a blocking minority, paving the way for the regulation to be formally voted – and likely adopted – on Tuesday.
Once the law is approved, the European Commission is expected to release more details of the deal and outline the next legislative steps to implement the e-fuel exemption.