The government of Mexico has informed the US Department of Homeland Security of its concern over a proposal to separate immigrant parents from their children in detention.
Foreign Minister Luis Videgaray said the measure could cause "irreversible harm" to many families.
US Homeland Security Secretary John Kelly said on Monday that the measure was being considered as a way to dissuade families from making the dangerous journey from Central America to the US with children.
Clarissa Martinez, vice president of the National Council of La Raza, said the measure would not make sense because of the cost of housing detainees.
In general, Central American immigrant families have been briefly detained together, processed and released to await their court date.