However tensions between communities on the US border have increased in recent months, with the number of border apprehensions spiking to 92,000 in March.
“We cannot allow racist and armed vigilantes to kidnap and detain people seeking asylum,” lawyers for the American Civil Liberties Union said in a statement.
New Mexico’s governor, Michelle Lujan Grisham said it was “completely unacceptable” that migrant families “might be menaced or threatened in any way, shape or form when they arrive at our border.”
The state’s attorney general, Hector Balderas, has also cautioned the group not to “attempt to exercise authority reserved for law enforcement.”
Jim Benvie, a spokesman for UCP, argued that the group’s actions are legal and akin to a citizen’s arrest.
Mr Benvie told the New York Times that the group intends to stay on the border until President Donald Trump’s proposed wall is built or Congress introduces tougher laws for asylum seekers.
“We’re just here to support the Border Patrol and show the public the reality of the border,” he said.
Mr Benvie refused to say how many members UCP has, but said the organisation includes people with military and law enforcement experience.