Energy Fuels has paused transport of uranium ore from its mine south of the Grand Canyon in Arizona to a processing facility in Utah—a path that crosses Navajo Nation land.

Members of the Navajo Nation are challenging the legality of uranium ore transport from a mine in Arizona across tribal lands to a processing facility in Utah.

A 2012 law bans uranium transport on the vast Navajo Nation land, which covers portions of Arizona, New Mexico, and Utah. Navajo Nation president Buu Nygren issued an executive order on Wednesday saying that there must be an agreement before uranium is transported through the reservation.

The Department of Energy’ Office of Legacy Management (LM) will be conducting verification and validation work at abandoned uranium mines in the Navajo Nation of northeastern Arizona during the fall field season, which runs from mid-October to mid-December.

The Environmental Protection Agency has awarded three contracts for cleanup efforts at more than 50 abandoned uranium mine sites in and around the Navajo Nation in the southwestern United States. The Navaho Area Abandoned Mine Remedial Construction and Services Contracts, worth up to $220 million over the next five years, were awarded to the Red Rock Remediation Joint Venture, Environmental Quality Management, and Arrowhead Contracting, the agency announced on February 11.

According to the EPA, the cleanup work is slated to begin later this year, following the completion of assessments in coordination with the Navajo Nation EPA, the tribe’s environmental agency. The sites are in New Mexico’s Grants Mining District and 10 Navajo Nation chapters. The companies selected have experience working on hazardous waste sites across the country, including cleaning up other abandoned mine sites in the Southwest, the EPA said.