When the U.S. Environmental Protection Agency announced the Clean Power Plan, it was destined for legal controversy. Not only does the policy form the spearpoint of President Obama’s strategy of fighting climate change through executive actions, it regulates carbon emissions from power production as a pollutant and requires each state to cut those emissions. That will mean the biggest shakeup in how the nation produces energy since the grid was built.

State governments swiftly launched a counterattack. Led by coal-producing West Virginia, 26 attorneys general have filed suit against the CPP, arguing it will wound the coal industry, make electricity more costly, and reduce the grid’s reliability. But even as lots of local leaders at the state level pushed back against the new policy, many officials at the municipal level embraced it with open arms.

That became clear in November, when 18 states announced they were supporting the plan. And it became clearer still on December 22, when the National League of Cities and the U.S. Conference of Mayors joined 13 cities and a county in filing a motion to participate in the case as amici curiae—in other words, they officially signaled their intention to contribute arguments to the case in favor of the EPA’s rule. About one third of the cities involved are located in states suing the plan, including Salt Lake City in Utah, Houston in Texas, and several cities in Florida.