BILLINGS, Mont. (AP) — U.S. officials have approved a 60-million ton expansion of a southeastern Montana coal mine that serves one of the largest power plants in the western United States, Interior Secretary Ryan Zinke's office said Friday.

The approval will extend the life of Westmoreland Coal Company's Rosebud Mine by 19 years and adds 10.5 square miles (27 square kilometers) to the 40-square-mile (104-square kilometer) strip mine, Zinke spokeswoman Heather Swift said.

The move comes as Westmoreland has seen its stock price plummet over the past year, prompting speculation the Englewood, Colorado-based company could be headed for bankruptcy.

Chief Executive Officer Kevin Paprzycki stepped down last month shortly after Westmoreland reported a $107 million loss through the first three quarters of 2017.

A Westmoreland representative did not immediately respond to a voice mail message seeking comment.

The Rosebud mine serves the 2,100-megawatt Colstrip power plant. The plant, located in the town of Colstrip, is a major employer in eastern Montana.

It plans to close two of its four electricity generating units by 2022, which means less coal would be needed from Rosebud.

The mine opened in 1968 and produced 8.8 million tons of coal in 2016. It employs about 330 people.

Environmentalists who have been seeking to close down the Colstrip plant opposed the expansion. They said burning the coal that would be mined would contribute to climate change.

A state district Judge last year ordered Montana environmental regulators to reconsider the mine's water discharge permit. The judge said state officials erred in reclassifying surrounding waterways so that they were subject to less-stringent pollution standards.