The American and British heirs of a consortium of Jewish art dealers filed suit last week against Germany and a German foundation seeking the return of a trove of medieval relics the dealers sold to the Nazis in 1935.

The plaintiffs’ complaint alleges that their ancestors parted with the items under duress and for substantially less than fair-market value.

The lawsuit, filed in U.S. District Court in Washington, D.C., is the latest move in a lengthy campaign by the heirs for return of the collection known as the “Welfenschatz,” or “Guelph Treasure” in English.

“It’s a challenging suit and we should expect a long and protracted fight. The plaintiffs certainly appear to have done their homework and asserted a number of compelling claims that could be successful,” said Joe Wielebinski, a shareholder in Dallas-based law firm Munsch Hardt Kopf & Harr, who represents victims of financial fraud, embezzlement and other white-collar crimes.

Wielebinski, who is not involved in the case, said it’s too early to predict the outcome. “The defendants are going to identify and assert a broad range of defenses, including possible challenges to the court’s jurisdiction, and will pursue them aggressively,” he said. “The plaintiffs appear to have anticipated some of these defenses.”

The objects at the heart of the dispute include gem- and pearl-studded silver and gold church artifacts, some of which are over 1,000 years old. The collection is currently worth an estimated $225 million to $275 million.

The Guelph Treasure was originally owned by several German aristocrats who sold the pieces to the Jewish art dealers in 1929. The dealers subsequently sold half the collection, then took the rest with them to Amsterdam when they fled the Nazis in 1934. The Nazis bought the remaining artifacts in 1935 for $2.5 million, according to an article published that year in The Baltimore Sun. The article said the treasures ended up under the control of Gestapo founder Hermann Göring, who presented them to Adolph Hitler as a “surprise gift.”

The sale price was only 35 percent of the real value of the works, according to the complaint. The heirs claim that the agreed sum was never fully paid and that their ancestors had no option but to sell, given the persecution and murder of the Jews by the Nazis.

“The choice they faced was clear: their property or their lives,” the complaint said.

The dispute differs from most claims for restitution involving artwork stolen by the Nazis in that there was a payment involved. Wielebinski said that the specific facts and circumstances surrounding the sale could be critical to determining the outcome of the matter, as the case involves a group of “sophisticated owners” who received some consideration for their property.