In what the New York Times called the world's largest unresolved Holocaust art claim, they are seeking the return of more than 40 works by masters such as El Greco, Lucas Cranach the Elder, Zurbaran, van Dyck, Velazquez and Monet.
The heirs of Hungarian banker Baron Mor Lipot Herzog filed the lawsuit on Tuesday in the United States District Court in Washington against the government of Hungary and several museums that it oversees.
Lawyers for the plaintiffs are also asking the Hungarian government for an accounting of all art, including paintings, sculptures and other works, from the Herzog family that it has in its possession.
"It's a very emotional subject," David de Csepel, a great-grandson of Baron Herzog, told the Times.
De Csepel is one of a dozen relatives of Herzog who is seeking return of the priceless works. He told the Times that the decision to file the suit came after decades of frustration with the Hungarian government.
"I want to see justice done. My great-grandfather was one of the most famous collectors in all of Europe. His passion and love of art is well known," said de Csepel, who lives in Los Angeles.
Michael Shuster, a lawyer for the Herzog family, said that Hungary had been "one of the countries that has been the most recalcitrant" about returning looted art.
"While other countries have cooperated," he said, "Hungary has been bucking that trend."
For more than two decades, Herzog's heirs have been petitioning the Hungarian government to return the art, valued at more than 100 million dollars, most of which has been hanging in Hungarian museums after being left there for safekeeping during World War II.
Other works were placed in the museums after being stolen by the Nazis and later returned to Hungary.
The requests have been rebuffed, as have appeals to the government from current and former United States senators over the years, including the Democrats Chris Dodd, Hillary Clinton and Edward Kennedy.
The Times wrote that a Hungarian court ruled in 2008 that the government was not required to return the art.
Gabor Foldvari, Hungary's deputy consul general in New York, told the Times in a telephone interview that "it was not the government's decision, but the court's decision" to keep the art.