Killsback said the tribe, which filed the lawsuit in US District Court in Great Falls, would be harmed by lifting the ban.
"The Northern Cheyenne rarely shares in the economic benefits to the region generated by coal industry and other energy development projects," he said.
About 386 million tonnes of federal coal are located near the Northern Cheyenne Reservation at the Decker and Spring Creek mines in Montana, the tribe said.
However, neighbouring tribe the Crow relies on coal production as its predominant industry and has called for the relaxation of coal regulations for years.
"A war on coal is a war on the Crow people," Zinke said on the call.
Legal group Earthjustice argued that lifting the coal moratorium imperils public health for the benefit of coal companies.
"No one voted to pollute our public lands, air or drinking water in the last election, yet the Trump Administration is doing the bidding of powerful polluters as nearly its first order of business," Earthjustice lawyer Jenny Harbine said.
The legal filing said that undoing the moratorium violates the National Environmental Policy Act, which requires a full environmental review prior to major policy changes.