The US Supreme Court has heard arguments over a collection of medieval artworks that Nazi Germany acquired from Jewish art dealers.
US descendants of the dealers allege the treasure trove, once owned by German royalty, was coerced out of their possession in a "forced sale".
With Germany's backing, the foundation that owns the pieces has called for the suit to be dismissed.
The collection is said to be worth at least $250m (£187m).
It has been on display in a Berlin art museum since 1963 and is now owned by the Prussian Cultural Heritage Foundation - the governmental entity that houses the collection.
The high court's ruling could open the door for foreigners to use US courts to litigate alleged injustices in their own countries.
The case centres on the Guelph Treasure, or Welfenschatz in German, a collection of 42 church art works - including altars, crosses and other Christian relics - made between the 11th and 15th centuries and passed down from one of Europe's oldest princely houses.
A consortium of Jewish art dealers purchased the entire collection a few months prior to the stock market crash of 1929, but sold most of the works at a reduced price in 1935 to the former German state of Prussia.