Sweden, Finland and Denmark are among the main supporters of the EU's emissions trading system, ETS, and are critical of the relief proposed by the European Commission.
However, several other countries, mainly in Eastern Europe but also, for example, Italy, are calling for even more flexible rules and measures to prevent the introduction of ETS2, a forthcoming expansion of the system to include housing and road transport.
Our proposal is to either postpone ETS2 or scrap it completely, says Estonian Prime Minister Kristen Michal on his way to the summit.
The dispute has caused Thursday's discussions to drag on as countries seek a statement that both sides can support.