At the heart of the dispute are the domestic-content requirements for projects installed under Ontario's FIT programme, which offer above-market guaranteed prices to renewable-energy producers.
In order to qualify, projects must meet a minimum percentage of their project costs using local goods and labour.
The made-in-Ontario requirement starts at 25% and increases to 50% by 2012 for wind projects. In the case of larger solar projects, the current 50% minimum jumps to 60% next year.
The EU, along with the US, has previously written to the WTO stating they should be involved in talks arising from Japan’s complaint. Under WTO rules, the EU and Canada need to enter talks over two months in order to resolve their differences.
Japan filed its own complaint in September last year. In July, the WTO agreed to set up a panel of judges to examine the issue.
In a statement about the EU complaint, a European Commission spokesperson said the Ontario FIT programme had affected European exports of renewable-energy products to the country.