The American Trucking Association scored a potentially big victory Friday in its battle with the Los Angeles and Long Beach ports over elements of their truck replacement programs.

The U.S. Court of Appeals issued a ruling reversing a lower court decision not to block the environmental program, which the trade association said could cause significant harm to the trucking industry.

“There is a likelihood of irreparable damages in this case,” the court said in its ruling. “We conclude that the concession agreements of both the ports will likely be found to be preempted in whole or in part.”

The ports recently kicked off their clean truck program, which is expected to reduce diesel truck emissions by up to 80 percent by replacing the oldest rigs with newer, cleaner vehicles. Last month, the ports began collecting a $35 cargo fee to help fund the program.

But the trucking industry has objected to certain elements of the program, especially a requirement that truckers cannot serve the port without gaining a taxi-like concession from each port. The industry also objects to a Port of Los Angeles provision requiring companies to hire drivers instead of using independent contractors.

Though Friday’s ruling does not immediately block the program, it suggests that at least portions of it will be enjoined soon unless there is an appeal.

However, port officials have said that no matter what the outcome of the lawsuit, it would not affect the ports’ requirement that truckers replace old polluting rigs with new, cleaner ones.

“The decision today does not change the legal status of our Clean Trucks Program or any other requirements currently in effect at the port,” said Richard Steinke, executive director of the Port of Long Beach, in a statement. “The port will continue to study the decision and appropriate next steps of the Court of Appeals, and anticipates that further proceedings will be held promptly before the District Court.”