When police found 15-year-old Mayra Laguna’s body in a canal in Hidalgo County, Texas, in February 1997, they settled on a culprit just hours later: her cousin, Ruben Cardenas Ramirez.

Cardenas is set to be executed on Nov. 8 after two decades on death row – only, as a Mexican citizen, his case is fraught with tremendous opposition from the neighboring nation, and has raised questions about the U.S.’s commitment to abiding by international law.

Mexico, which has funded the defense, has mounted an eleventh hour campaign to stay the execution.

“It’s a significant treaty violation,” Gregory Kuykendall, an Arizona attorney authorized to speak on behalf of Mexico, told the Houston Chronicle on Thursday.

In executing Cardenas, Texas officials could be in violation of an international law known as the Vienna Convention on Consular Relations.

After Hildago County authorities arrested Cardenas, they reportedly failed to alert Mexico, and allegedly neglected to notify the defendant of his right under the convention to speak to his country’s diplomats.

In 2004, the U.N.’s international court in the Hague ruled that the U.S. must review cases to determine if such oversights impacted the convictions. Then-president George W. Bush directed states to comply, but the Supreme Court overruled his order. Only Congress can require states to follow the international court’s ruling, and there has been no such intervention in Cardenas’s case.

Cardenas’s defense counsel Maurie Levin argued to the Chronicle that the disregard for the convention changed the course of her client’s trial. Had Cardenas’s government been permitted to aid him instead of finding out about the case five months later, the defendant may not have given false confessions, she said.

Cardenas’s is far from the first instance of the U.S. executing a Mexican citizen. Previous cases have strained the two nations’ ties, and Mexico, which does not have capital punishment, has even launched a fund called the Mexican Capital Legal Assistance Program to help save it’s citizens from the U.S. death penalty.

But the latest episode stands out with allegations of miscarried justice. In the face of the charges – the abduction, rape and murder of his cousin — Cardenas has repeatedly claimed innocence, while the defense has claimed allegedly coerced confessions, what it calls inconclusive forensics and reportedly conflicting witness accounts.

Mexico has not weighed in on the innocence or guilt of the convicted man, focusing instead on the treaty violations. The U.S. Department of State reportedly met with Hidalgo County prosecutors over Cardenas’s case in February, but the Nov. 8 execution by lethal injection remains set.

Cardenas would be the 166th inmate to be executed by Texas in the past decade, and the 11th Mexican national to be executed in the U.S. since 1979, according to the Death Penalty Information Center.

Get The Brief. Sign up to receive the top stories you need to know right now. Please enter a valid email address. Sign Up Now Check the box if you do not wish to receive promotional offers via email from TIME. You can unsubscribe at any time. By signing up you are agreeing to our Terms of Use and Privacy Policy . This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. Thank you! For your security, we've sent a confirmation email to the address you entered. Click the link to confirm your subscription and begin receiving our newsletters. If you don't get the confirmation within 10 minutes, please check your spam folder.

Write to Laignee Barron at Laignee.Barron@time.com.