NorthWestern Corp. entered into a six-year agreement to supply the Colstrip power plant in Montana with coal from Westmoreland Rosebud Mining.

The Rosebud mine, an operation controlled by Westmoreland Mining Holdings LLC that sits adjacent to the power plant, would begin supplying coal under the new deal beginning Jan. 1, 2020, according to a Dec. 5 release from NorthWestern. The new contract replaces one expiring at the end of 2019.

The deal will allow Colstrip to meet peak demand for its Montana customers, according to the release.

Westmoreland Mining Holdings took over the mine earlier in the year, after Westmoreland Coal Co. filed for bankruptcy protection.

The mine exclusively serves the plant, which intends to close two of its units by the end of the year. The U.S. Office of Surface Mining Reclamation and Enforcement approved a proposed expansion to the mine in June, to which environmental groups have objected, noting that its only customer will demand less coal in the years to come.