ALBUQUERQUE, N.M. (AP) - New Mexico environmental regulators have approved a permit change that could ultimately allow for more waste to be placed at the U.S. government's only underground nuclear waste repository.

The state Environment Department approved the change Dec. 21. It had been requested months ago by the U.S. Energy Department and the contractor that operates the southern New Mexico facility.

The Albuquerque Journal reports the approval came just days before Gov. Susana Martinez leaves office. Watchdog groups have accused the administration of rushing a decision and they plan to appeal.

The permit modification changes the way the volume of waste is calculated. Specifically, it excludes the empty space inside waste packaging containers.

Critics also are concerned that this could be a first step in expanding the repository's mission to hold other kinds of waste.