NEW YORK. Dutch museums--including the Rijksmuseum, Frans Hals Museum and Mauritshuis--could lose up to 227 works, if a restitution claim by the heirs of the Dutch Jewish art dealer Nathan Katz is successful. Research being conducted as a result of the claim is also shedding new light on the actions of the Dutch government in the post-war period in relation to art which may have been looted by the Nazis or acquired in forced sales. In March, four heirs of Mr Katz filed a claim for the return of 225 paintings and two tapestries currently held in Dutch museums--although the information only became public at the end of September when Dutch museum directors were notified by the ministry of culture of the claim. This is the biggest restitution case in Dutch history, even larger than the claim of Marei von Saher, the heir of Jewish dealer Jacques Goudstikker who in 2006 secured the return of 202 works from the Dutch government. She is now pursuing a lawsuit against the Norton Simon Museum in California. The Katz claimants, Sybilla Goldstein-Katz of Florida and her siblings David, Eva and Margaret who live in Europe, are seeking restitution for art owned by their father who they believe was forced to sell much of his collection after the Nazi occupation of Holland in May 1940. The bulk of the works were sold to Alois Miedl, an agent for art collector and Nazi Reichsmarshall Hermann Göring. After World War II, the Dutch State received several thousand works of art that were forcibly sold, robbed or confiscated by the Nazis, from Germany and the Allies. These works are designated as the Nederlands Kunstbezit-collectie [NK Collection]. While many of these pieces were returned to their owners in the years directly after the war, the remaining objects with questionable provenance were placed on long-term loan to the nation's most prominent museums. However, Tina Talarchyk, a Florida-based attorney representing the Katz heirs, says she has also found evidence that the government was selling works as late as 1981. Roman Capriccio, 18th century, by Panini, was sold at auction in 1981, but is listed as being sold by Katz to Miedl in 1940. Ms Talarchyk also claims that the Dutch state archives record the existence of "a bright blue inventory book recovered from Galerie Katz", listing the works then in Nathan Katz's possession. The book has not been found. The claim has aroused heated debate in the Netherlands which stands to lose large numbers of old master paintings including important works by Jan Steen, Gerrit Dou, Nicolaas Maes and Jacob Ruisdael. The paintings in question include four pieces in Amsterdam's Rijksmuseum most significantly Gerbrand van den Eeckhout's The Continence of Scipio (around 1652), which, like several of the works on the list, was purchased from Katz specifically for Adolf Hitler's Führermuseum in Linz. Also at the Rijksmuseum is Pieter de Molijn's De Wolfabricage (1651), Cornelis van Haarlem's Pomona receiving the Harvest of Fruit (1626), and a still-life by Jan van de Velde III. Other museums affected include the Dordrecht, Fries, Frans Hals and Centraal museums, as well as the Mauritshuis in the Hague.Ms Talarchyk told The Art Newspaper: "While we understand the emotional attachment by the art museums and the Dutch State to these works of art, that doesn't change the fact that the pieces belong to the Katz family and should be returned to their rightful owners." The claim is being reviewed by the Dutch Restitutions Committee, a group of experts responsible for advising the government on the return of cultural property. According to Evelien Campfens, a spokeswoman for the commission: "The success of the claim is dependent on establishing the involuntary sale of the works." She added that art sold after the occupation of Holland in 1940 is given special consideration however: "It is more difficult to prove the involuntary sale of objects by art dealers than by private collectors, because their primary goal is to sell works of art." It is expected that the claim could take at least ten months to resolve.