Updated

The Supreme Court ruled unanimously Monday that the Bush administration can skip a lengthy environmental study and open U.S. roadways to Mexican trucks as soon as it wishes.

The high court ruled against labor and environmental organizations that have long fought expansion of Mexican trucking within the borders of the United States despite a guarantee this country made when it signed the North American Free Trade Agreement (search) more than a decade ago.

Ruling on narrow procedural issues, the Supreme Court said the president has authority to open the border, and a federal agency responsible for truck safety has no say in the matter. Thus, the agency was under no obligation to study environmental effects from opening the border, as a lower federal court had ordered.

As a practical matter, Monday's ruling may mean little. The Bush administration had already begun the court-ordered study and is expected to complete it soon. The study could only delay, not prevent, the border opening, and the White House had already said that it would let the trucks roll as soon as it was free to do so.

President Bush ordered the opening of all U.S. roads to Mexican trucks in 2002, but the dispute has been tied up in courts.

The long fight, begun during the Clinton administration, had ground down to a last quarrel over an environmental assessment, or study, called an EA. Opponents of the truck expansion argued that a particular kind of study was required by law and that the Bush administration was ducking that requirement.

The justices said no, and also rejected what they called the opponents' attempts to make the case about safety and environmental concerns instead of about precise legal requirements.

"Because the president, not the (Federal Motor Carrier Safety Administration (search)) could authorize or not authorize cross-border operations from Mexican motor carriers, and because FMCSA has no discretion to prevent the entry of Mexican trucks, its EA did not need to consider the environmental effects arising from the entry," Justice Clarence Thomas wrote for the court.

NAFTA, signed in 1993 by the United States, Mexico and Canada, allowed Mexican trucks to eventually use a large portion of U.S. roads. Mexican trucks are limited now to commercial border zones, forcing long lines at border crossings and complicated transfers of goods being shipped from Mexico to the United States.

Under NAFTA, Mexican trucks were to have gained full access to U.S. roads beginning in 2000. But the Clinton administration, under pressure from labor and consumer groups, refused to grant them entry. Mexico successfully challenged the moratorium through a free trade tribunal.

The California-based 9th U.S. Circuit Court of Appeals (search) had ordered the government to do a $1.8 million study, which was expected to run a year or more. It was not immediately clear whether the study would continue after Monday.

The Bush administration had appealed to the high court for help, arguing that the two-decade moratorium on Mexican trucks should end.

The ruling ends a challenge from the consumer group Public Citizen (search), the Teamsters union and others who had sued on safety and environmental grounds. The opponents argued that Mexican trucks are typically older and more polluting than American trucks.

Mexican trucks make approximately 4.5 million border crossings every year. Mexico claims the moratorium has cost it more than $2 billion.

The case is United States v. Public Citizen, 03-358.