BILLINGS, Mont. (AP) — A federal judge says the U.S. Interior Department should not have approved the expansion of a Montana coal mine before taking a closer look at its environmental impacts.

U.S. Magistrate Judge Carolyn Ostby says work at the Spring Creek Coal mine near Decker will not be shut down immediately. Rather, the judge recommended in a Friday ruling that federal officials go back and reconsider the environmental effects of the expansion by Wyoming-based Cloud Peak Energy.

Environmental groups sued the Interior Department following its 2012 approval of the expansion.

Cloud Peak spokesman Rick Curtsinger says the company is disappointed in the ruling and plans to work with federal officials to defend the expansion.

Similar cases involve the San Juan coal mine in New Mexico and the Colowyo and Trapper mines in Colorado.