Poland, Hungary and the Czech Republic were threatening on Thursday to wreck the European Union's new push for climate neutrality by 2050, just a day after the bloc's executive trumpeted it as Europe's "man on the moon" moment.
The 27 EU national leaders will meet in Brussels and push to agree to put their bloc on net-zero greenhouse gas emissions by mid-century, luring the reluctant eastern member states with extra money to transform their economies.
But a senior diplomat from one of those hesitant countries said of the latest draft summit decision: "For us, it definitely does not go far enough. Both in terms of nuclear, but also on burden-sharing and financial support."
Another EU diplomat estimated chances for an agreement at the summit - which must be unanimous - at 50/50.
The tussle comes a day after the bloc's executive proposed a Green Deal to mobilise 100 billion euros worth of investment to help the bloc's economies move away from fossil fuels.
But the poorer Poland, Hungary and the Czech Republic were not on board, demanding that any decision spells out in more detail the scale and scope of financing available, and pushing to include funding for nuclear energy in the EU's fresh push to cut emissions.
"There will certainly be an amount of arm-wrestling," said a second senior EU diplomat from a country more enthusiastic about the 2050 goal. "There will have to be new money... but some member states will be less than enthusiastic about the target of raising 100 billion euros."
Underlining divisions in the bloc on climate, EU national diplomats in Brussels on Wednesday blocked a set of new rules governing which financial products can be called "green" and "sustainable".
The Czech Republic generates about half of its electricity from coal and wants to phase most of it out over the next 20 years, replacing part of it with new nuclear power plants.
Hungary relies on nuclear for about a third of its energy needs, with coal making up less than 15% of its energy mix. It wants to abolish coal by 2030 and replace it with a mix of nuclear, gas, renewables and energy imports.
Poland produces some 80% of its power from coal and discussions about introducing nuclear energy have not yet been settled, partly due to high costs.
In Brussels on Thursday, the three will be pushing against countries like Germany, committed to abolishing nuclear power.
The climate discussion feeds into another tricky debate, over the next long-term budget.
No agreement is expected on that after a proposal by the bloc's current president Finland to cap joint spending at 1.087 trillion euros for 2021-27 was rejected by both the frugal camp and those seeking heavier outlay. The leaders might agree, however, to hold a summit next February to seal a deal.