HUMBERTO LEAL JR., who was executed in Texas on Thursday, was one of 40 Mexican nationals on death row in the United States who were not advised of their right to consular access under the Vienna Convention for Consular Relations. The United States, as one of about 160 countries that signed the treaty, is obligated to notify foreign nationals who are arrested in the United States of their right to speak with their embassies. U.S. citizens have the same rights if they are arrested in a country that is also a signatory, which may be particularly important in countries that do not routinely allow defendants access to lawyers.

In an extraordinary move, the Obama administration had asked the Supreme Court to stay Mr. Leal’s execution. The request was intended to give Congress a few months to move on legislation that would have addressed the Vienna Convention breach. That legislation, introduced by Sen. Patrick J. Leahy (D-Vt.) in June, would have allowed Mr. Leal and the 39 other Mexican nationals a one-time special hearing before a federal court judge to determine whether the failure to allow consular access significantly harmed their ability to defend themselves. The hurdles would have been high, meaning that few, if any, would have been likely to win new trials. Mexico joined in asking the court for a stay, as did former U.S. diplomats from Republican and Democratic administrations.

The Supreme Court denied the request in a 5 to 4 unsigned opinion. The court concluded that it had the obligation “to rule on what the law is, not what it might eventually be.”

Justice Stephen Breyer, writing for the four dissenters, had the better argument when he noted that the court had substantial leeway to order a temporary stay. The circumstances were especially compelling, Justice Breyer noted, because of the administration’s assertions that failure to stop the execution would put “the United States in irremediable breach of its international-law obligation” and could trigger “serious repercussions for United States foreign relations, law-enforcement and other cooperation with Mexico and the ability of American citizens traveling abroad to have the benefits of consular assistance in the event of detention.”

Although we disagree with how the court disposed of this case, the majority makes a critical point: It has been seven years since the judicial arm of the United Nations found that the United States violated the Vienna Convention by not notifying Mr. Leal and his compatriots of their rights to consular access. It should not take another seven years before Congress acts to remedy the situation.