The denial of birth certificates to U.S. citizen children born to immigrant parents 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.

The Mexican government filed its amicus brief late Monday in support of a coalition of undocumented parents who are suing the state of Texas after they were denied birth certificates for their children.

The brief says that “friendly nations” have a history of accepting foreign passports or government-issued IDs to facilitate the identification of a foreigner.

“Conversely, expressions of doubt about the integrity of documents issued by a friendly country introduce a troublesome and discordant element into binational or transnational relations,” the 19-page court document states. 

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Attorneys with the Texas Civil Rights Project and Texas RioGrande Legal Aid filed the lawsuit against the Department of State Health Services on behalf of six U.S. citizen children and their parents who are undocumented immigrants from Mexico, Honduras and Guatemala. The original complaint was filed in May and has been amended twice to include more than 30 families. La Unión Del Pueblo Entero, or LUPE, an immigrant rights group with about 7,000 members, has also joined the lawsuit.

At issue is the refusal by county registrars’ offices to accept the parents' foreign passports as a valid form of identification without a valid U.S. visa or consular identification card. The families claim the state has violated the 14th Amendment’s Equal Protection Clause by rejecting the documents, and is also violating the Supremacy Clause by enforcing federal immigration laws.

The Texas attorney general’s office, which is representing the health services department, has asked the court to dismiss the lawsuit, claiming the agency is protected from the litigation by the 11th Amendment. Under its sovereign immunity provision, the state cannot be sued in federal court because it has not waived that right, according to court documents. 

Legal experts have called that strategy predictable and commonplace, but also say it’s likely to fall short and predict the case will proceed.

The state health services department has said repeatedly that matrícula cards — issued by the Mexican consulate offices throughout Texas — were never considered secure documents for purposes of obtaining a vital record. Some counties were accepting the IDs until recently, however. They have been ordered to stop by the department.

The Mexican government’s brief specifies that it supports the plaintiffs’ request for an emergency injunction to require the state to name two forms of ID that are “reasonably and actually accessible” for the parents. That request was made Friday.

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“Our argument isn’t ‘yes matrícula, no matrícula,’” said attorney Jennifer Harbury, who represents the families. “The argument is ‘what will you take that people can actually get?’ They have to take something. [The children] were born here. They are U.S. citizens.”

The amicus brief also claims that denying the children U.S. birth certificates also blocks their claims to Mexican citizenship. A child born to Mexican parents has that right but must show proof of identity. Infringing on that is a violation of international law, the brief states.

On Monday, Consul Carlos González Gutiérrez from the Mexican Consulate General’s office in Austin said the matrícula contains biometric technology that makes it more secure than driver’s licenses in some U.S. states. He also said a passport — even without a current U.S. visa — should be valid proof of one’s identity. Whether someone is in the country legally should not matter when a parent is trying to obtain a birth certificate, he added.

“We think that they are not immigration authorities,” he said. “The passport is the official way to identify oneself.”

González gave a sworn affidavit attesting to the validity of the Mexican documents that was included in Monday's filing.