Mexico City, Mexico - Mexico fears that a contentious Texas immigration law will lead to unjust harassment, detention, deportation and criminalization of its citizens, it told a US court on Thursday.

The law, which is caught up in a legal back-and-forth in the United States, would allow state police to arrest and deport migrants who cross over illegally from Mexico.

(FILES) Migrants walk between Concertina wire and a string of buoys placed on the water along the Rio Grande border with Mexico in Eagle Pass, Texas, on July 16, 2023, to prevent illegal immigration entry to the US. The US Supreme Court lifted its hold March 19, 2024 on a controversial Texas law that would allow state police to arrest and deport migrants who cross illegally into the United States from Mexico. (Photo by SUZANNE CORDEIRO / AFP)

Known as Senate Bill 4, it is strongly opposed by President Joe Biden's administration, which argues that the federal government has authority over immigration matters, not individual states.

Mexico, also a vocal critic of the law, on Thursday submitted a "friend of the court" or "amicus curiae" brief to the US 5th Circuit Court of Appeals.

It outlines Mexico's "concern that the law could lead to the undue harassment, arrest, expulsion and criminalization of Mexican citizens and individuals who 'look Latino' by Texas agents," the foreign ministry said.

The law "creates an atmosphere of uncertainty, fear and vulnerability" and "violates Mexico's sovereign right to determine its own policies regarding which individuals enter our territory," it added.

A federal judge last month temporarily blocked the law passed by the Republican majority in the Texas state legislature, saying it "conflicts with key provisions of federal immigration law."

But a conservative-dominated appeals court said Senate Bill 4 could go into force unless the Supreme Court ruled otherwise.

The nation's highest court, which has a 6-3 conservative majority, issued a temporary stay on SB 4 earlier this month but lifted it Tuesday, allowing it to take effect while legal challenges play out in lower courts.

But by Tuesday evening, the 5th Circuit Court of Appeals put the law back on hold.

Mexico has warned that it will not accept deportations by Texas, whose Republican governor Greg Abbott has decried an "invasion" at the southern border.

US Republicans blame Biden for the recent record flow of migrants into the United States.

More than 2.4 million migrants crossed the southern US border in 2023 alone, largely from Central America and Venezuela as they flee poverty, violence and disasters exacerbated by climate change.