One of the largest coal-fired power plants in the western United States is inching toward an eventual shutdown amid crippling competition from cheap natural gas and renewable energy sources.

The Associated Press reports the Colstrip Steam Electric Station in Colstrip, Mont., will close two of its four units by the beginning of this week, or as soon as they run out of coal. The plant has been unable to compete with other cheaper forms of energy and operating costs have risen due to mandates for stricter pollution controls.

The plant employs around 300 people and is the lifeblood of the economy for the nearby town of Colstrip, which is home to about 2,300 people. Talen Energy spokeswoman Taryne Williams told AP that employees will be re-assigned to decommissioning work going through the middle of this year, but there’s no “hard and fast numbers or timelines” as the company considers how many workers it will need for the two remaining units.

The two units that are shutting down are operated by Pennsylvania-based Talen, which co-owns them with Puget Sound Energy, and were built in the 1970s.

The AP reports that large amounts of ash from burning coal at Colstrip has contaminated underground water supplies with toxic materials and will cost hundreds of millions of dollars to clean up. The Montana Department of Environmental Quality is currently working on plans to clean up the material.

The six utilities that own shares of the two remaining units are making plans to stop operations as soon as 2025.