There is some famous scholarly debate on whether WTO dispute settlement rulings are binding. Here's a media take on it, from the CBC news (in the context of the Ontario feed-in-tariff case):
The World Trade Organization appears to have upheld a complaint against the Province of Ontario’s green energy program.
The complaint was made by the EU and Japan, which claim the province's "feed-in tariff" program for its energy grid discriminates against foreign component manufacturers by declaring a minimum percentage of renewable energy goods and services be provided by Ontario-based companies.
...
Although the WTO has yet to acknowledge any decision publicly, reports Monday suggest the affected parties have been notified of the organization's decision to side with the complainants.
...
The WTO ruling is non-binding, meaning Ontario could simply ignore it and not face any monetary punishment. But such a move would likely be met with the implementation of tariffs against any Ontario-made goods in Japan and the EU.
So, as they put it, a WTO ruling is "non-binding," but tariffs could be imposed as part of the enforcement.
I tend to think that the word "binding" does not tell us that much in this context. Rather, the key question is how effective the enforcement mechanism is.
