Pennsylvania lawmakers proposed another $500 million plan to subsidize the state’s nuclear industry and fought back against critics of providing support.

Pennsylvania lawmakers must approve nuclear subsidies by May to prevent the retirement of Three Mile Island Unit 1, Exelon CEO Chris Crane said.

The closure of four nuclear plants in Pennsylvania and Ohio would boost power prices and carbon emissions, undoing the clean air benefits of renewables, according to a Brattle Group report.

Exelon announced that it will retire Three Mile Island Unit 1 in September 2019 “absent needed policy reforms.”