Via Sallie James of Cato, I came across this story:
Minnesota recently enacted a plan to tax electricity generated by carbon-intensive methods in North Dakota--specifically, a carbon fee of $4 to $34 per ton of CO2 emissions in addition to the normal cost of coal power.
Naturally, North Dakota's utilities are none too happy about this development. The state rightly claims that the tariff will discourage Minnesota from buying power from North Dakota, which produces the majority of its energy from coal. State officials say that the state is working on carbon capture technology as well. And the state isn't taking Minnesota's tariff lying down--North Dakota is suing Minnesota since it believes the tariff, scheduled to go into effect in 2012, is an illegal attempt to regulate out-of-state utilities.
More here. I'm not sure the lawsuit has actually started yet, but if it goes ahead the dormant commerce clause issues could be a preview of cases to come at the WTO.