(Reuters) - Pennsylvania state Representative Tom Mehaffie introduced legislation on Monday that would compensate the state’s nuclear reactors for the zero-carbon energy they produce, in an effort to provide the plants with enough revenue to stay open.

Nuclear power plants in Pennsylvania generate 42 percent of the state’s electricity and provide 93 percent of its zero-carbon electricity. But they were not among the 16 forms of energy projects included in the state’s Alternative Energy Portfolio Standards (AEPS) program, which requires energy suppliers to buy credits that help fund wind, solar and other projects.

Mehaffie, a Republican whose district is near the Three Mile Island reactor, said his proposed Keep Powering Pennsylvania Act will recognize the value of nuclear as well as other zero-emission generation resources. It would make Pennsylvania the fifth U.S. state after New York, Illinois, Connecticut and New Jersey to provide a new revenue stream to keep nuclear reactors in service to reduce greenhouse gas emissions.

Mehaffie said the bill would cost about $500 million, which he said would be much less than the $4.6 billion it would cost the state in higher electric bills and lost jobs, tax revenue and other costs if the reactors were allowed to close.

He said the typical residential power customer’s bill would only increase by $1.77 per month under his bill versus $2.39 if the reactors close.

Electricity prices have been depressed due to cheap natural gas from shale fields, including the Marcellus in Pennsylvania, and increased use of renewable power such as wind and solar. This has made some nuclear plants uneconomical, and U.S. nuclear operators have shut several reactors over the past five years.

Exelon Corp said it plans to shut the Three Mile Island nuclear plant by September 2019, while FirstEnergy Corp said it plans to shut the Beaver Valley reactors in 2021 if they cannot operate profitably.

Pennsylvania’s five nuclear plants account for nearly 16,000 jobs and provide $69 million in net state tax revenues annually, Mehaffie said.

Exelon operates two reactors at the Peach Bottom power plant, two at Limerick and one at Three Mile Island, FirstEnergy operates two reactors at Beaver Valley and Talen Energy owns two at Susquehanna.

In addition to Pennsylvania, officials in Ohio are considering similar rules to prevent its reactors from retiring early, and officials in U.S. President Donald Trump’s administration are also looking at programs to keep nuclear and coal plants operating longer.