Under an order from the Illinois Commerce Commission, Ameren Illinois must pay $48.1 million to its customer base across the state, the Peoria Journal Star reports.

According to the news source, the ICC made the announcement earlier in the week, and was spurred by a review of the utilities proposed utility rate hikes, which it said would be to pay for its ambitious smart grid plan. The utility hoped to raise the rates as part of its $625 million plan to modernize the state's aging electric infrastructure, however this was rejected by Illinois regulators, who asked the utility for more details on the proposal.

"The commission's decision, a 3-2 vote, follows months of review of major financial issues," said ICC spokeswoman Beth Bosch.

Leigh Morris, a spokesman for Ameren, said the utility was dissatisfied with the ICC ruling.

"We believe it was a very sound filing. We'll be filing for a rehearing," he said.

Due to the decision, Ameren Illinois customers will see a decrease in electricity rates that will go into effect in January.

Illinois is home to a thriving competitive energy market that has sprouted several retail energy providers, all of which are competing with the state's utilities and helping to keep electricity rates low.