Cosmetics heir and museum patron Ronald Lauder has enlisted the Washington, D.C. lobbying firm American Continental Group (ACG) to assist in his campaign to get museums to return Nazi-looted art to the heirs of its original owners, reports O’Dwyer’s, based on a public filing.

Lauder is the president of the World Jewish Congress and the founder of New York’s Neue Galerie. He has been outspoken on this issue, warning the Kunstmuseum Bern last year that it would be met with an “avalanche” of lawsuits if it accepted the donation of the collection of the late Cornelius Gurlitt, which contains art seized by the Nazis. He also published an editorial in the Wall Street Journal in 2014 declaring that it is “time to evict Nazi-looted art from museums.”

He told the New York Observer in May that the next front in the battle for restitution is to get Germany and Switzerland to comb through their museums’ collections in search of Nazi-looted works. Lauder also has a background in Washington, having served as the U.S. ambassador to Austria under Ronald Reagan.

A former chairman of the Museum of Modern Art, Lauder paid $135 million for Gustav Klimt’s Portrait of Adele Bloch-Bauer in 2006. His collection reportedly encompass 4,000 pieces, including works by artists such as Joseph Beuys, Constantin Brancusi, Wassily Kandinsky, Anselm Kiefer, Gustav Klimt, Henri Matisse, Pablo Picasso, and Gerhard Richter. Forbes lists the worth of the collection at $1 billion.

ACG lists clients including Ernst & Young, Hewlett-Packard, Monsanto, and Random House. Shawn Smeallie, a partner with the firm, will work with Lauder. Smeallie has been with the firm for 20 years. Before joining ACG, he was special assistant for legislative affairs to President George H.W. Bush and special assistant to the director for legislative affairs at the Office of Management and Budget.