The Supreme Court is making it harder for a multimillion-dollar lawsuit involving centuries-old religious artworks obtained by the Nazis from Jewish art dealers to continue in U.S. courts.

The court ruled unanimously Wednesday in a case involving the 1935 sale of a collection of medieval Christian artwork called the Guelph Treasure. The heirs of the art dealers contended the sale of the works, now said to be worth at least $250 million, was done under pressure. Germany disagreed and argued that the case did not belong in the American legal system.

The justices said the heirs had not at this point shown that federal law allowed them to bring their case in U.S. courts. The court sent the case back for additional arguments.

Because of that ruling, the Supreme Court also sent a similar case involving a group of Hungarian Holocaust survivors back to a lower court. They were seeking to be compensated for property taken from them and their families when they were forced to board trains to concentration camps.