The concern was raised in an amicus brief filed Monday evening to lend support to immigrants parents who sued Texas after being denied birth certificates for their U.S.-born children, even after showing their "matrículas," the ID cards issued by the Mexican consulate to undocumented immigrants.

Mexico says the practice stands in stark contrast to the historical practice among countries to accept passports or other forms of ID to issue birth certificates.

[It] not only jeopardizes their dignity and well-being, but could threaten the unique relationship between Mexico and Texas, the Mexican government said in a brief tied to a lawsuit filed against the state by Texas Civil Rights Project and Texas Rio Grande Legal Aid.

The lawsuit, the Texas Tribune reported, was filed on behalf of six U.S. citizen children and their undocumented parents, who came from Mexico, Honduras and Guatemala. Other groups since have joined the suit.

A main point of contention is the all-out refusal at some county registrars offices to accept as a valid form of ID anything short of a U.S. visa or consulate ID card, the Tribune said.