New Mexico Attorney General Gary King says the federal government has sided with Texas in an effort to take the state's groundwater.
King responded Tuesday to a motion by the government to intervene in a dispute over management of the Rio Grande. Texas first took the case to the U.S. Supreme Court more than a year ago.
New Mexico maintains it is meeting its water delivery obligations to Texas.
But the federal government alleges groundwater pumping in New Mexico is tapping the shallow aquifer that would otherwise drain back into the Rio Grande and flow to Texas.
In the latest court filing, King claims groundwater is a separate source of water from the Rio Grande Project, which provides farmers in southern New Mexico and Texas with irrigation water.