The Energy Department’s top independent analysts are working on a study of the administration’s landmark proposal to curb carbon pollution from existing power plants.

The Energy Information Administration (EIA) said on Friday that the study will look at the rule, which was first proposed in June by the Environmental Protection Agency (EPA), and the impact it will have on utilities.

{mosads}Jonathan Cogan, spokesman for EIA, called the report a “complex and challenging task.”

EIA plans to finish it by early 2015, he added.

Opponents of the rule argue it will strain utilities’ ability to turn to cheaper energy sources like coal, because the EPA requires each state to hit certain reduction targets.

The EPA argues that the rule is extremely flexible and that it is working with states to find the best design that fits their energy portfolio.