That, according to the Hague, was a violation of a 1963 treaty known as the Vienna Convention.

"We find ourselves in an unusual position," Texas Solicitor General Ted Cruz told the Houston Chronicle. "Texas is not regularly litigating against the United States. But sadly enough, the United States will appear alongside Medellin at the argument."

Medellin v. Texas will be argued Wednesday and could determine the fate of Medellin and 50 other Mexican killers on death rows in the United States, including more than a dozen in Texas. All of them say they were not told of their right to contact Mexico for legal help.

The court is expected to produce a ruling clarifying which powers reside with the president, Congress and courts, which powers belong to the federal government versus the states, and what the relationship is between international and domestic law.

The Bush administration became involved in the Medellin case in 2003 when Mexico sued the U.S. over the consular issue in the International Court of Justice at the Hague. The so-called "World Court" is the United Nations' top court for resolving international disputes.

The court ruled in Mexico's favor in late 2004 and ordered the U.S. to reconsider the Mexican inmates' murder convictions and death sentences. In February 2005, Bush announced that while he disagreed with the World Court's decision, the U.S. would comply. He ordered courts in Texas and elsewhere to review the cases.

A few days later, however, the president withdrew the U.S. from the part of the Vienna Convention that gives the World Court final say in international disputes.

The Supreme Court, which had agreed to hear Medellin's case, dismissed it later in 2005 to allow the case to play out in Texas. Last November, the all-Republican Texas Court of Criminal Appeals balked at the president's order, saying Bush had overstepped his authority.

The Texas court said the judicial branch, not the White House, should decide how to resolve the Mexican cases. It also said Medellin wasn't entitled to a new hearing because he failed to complain at his original trial about any violation of his consular rights and had therefore waived them.

Medellin appealed again to the U.S. Supreme Court, which announced last May it would hear his case. His lawyer, Donald Donovan of New York, will argue this week that Bush was correct when he took action to comply with the World Court's decision.

The Bush administration, now siding with Medellin and Mexico, will try to help Donovan's team convince the justices that the Texas court is undermining the president's efforts to conduct foreign policy.

Cruz, who will argue the case for Texas, called Bush's unprecedented attempt to issue orders to the judicial branch – and the state courts in particular – "breathtaking."

"It is emphatically not the province of the president to say what the law is," he told the Houston Chronicle. "If this president's assertion of authority is upheld in this case, it opens the door for enormous mischief from presidents of either party. What might these presidents be inclined to do if they had the power to flick state laws off the books?"

Meanwhile, Randy and Sandra Ertman, the parents of one of Medellin's victims, also have weighed in. In a court brief filed on their behalf by the California-based Criminal Justice Legal Foundation, the Ertmans argue that their 14-year-old daughter's rights, and the rights of other victims, will be given short shrift if the justices further delay the "already long-overdue execution of this well-deserved sentence."

"This case has produced much lofty discussion about international law and the separation of powers. We must not forget, though, that this case is about a real crime against real people," they wrote. "Enough is enough."