BRUSSELS — The European Union’s most important climate policy is up for review this summer, and Ireland must be the go-between in a major ideological contest among member countries.

The European Commission will release a hotly anticipated review of the Emissions Trading System in mid-July, barely two weeks into Ireland’s presidency of the Council of the EU.

Months of arguing will follow among member countries over how far to water down the 20-year-old policy, a cap-and-trade scheme designed to reduce the emissions of the EU’s most polluting industries by making them pay for each ton of carbon they emit.

Already, the review has become intensely political. As soon as U.S. and Israeli bombs fell on Iran and oil and gas prices skyrocketed, a gang of 10 EU member countries — led by Poland, Italy, Czechia and Austria — released a letter characterizing the ETS as a plague on household energy bills, a business killer and a constrictive mandate for European decarbonization.

Since then, other countries have piled in. On the moderate side, France, Germany, Spain and others are now also arguing the ETS requires reform so the private sector can catch its financial breath amid market uncertainty. But Sweden, Denmark, Finland and the Netherlands — among the biggest defenders of the ETS — kept their signatures off a pair of critical papers to the attention of the Commission in May.