A giant coal power plant in northeast Arizona could close within the next few years.

Costs of new regulations, coupled with the falling price of fuels like natural gas, are some of the reasons the Navajo Generating Station could eventually shut down. The lease is set to expire in 2019. Owners of the plant, including the federal government, the Salt River Project, Arizona Public Service, are mulling whether or not to keep it open it after that, or possibly close it sooner.

“If a decision was made to decommission the plant, the owners could consider when during that four-year period that might occur, but that decision has not been made,” Scott Harelson with SRP told KJZZ.

Harelson’s comments come in response to a claim by a Navajo environmental advocacy group that the owners are threatening to close the plant before the lease expires to extract concessions from the Navajo Nation.

Harelson says that’s in no way true.

The plant employs about 500 people and emits more greenhouses gases than almost any other power plant in the country.