Robert De Niro is suing a New York art dealership after it sold his late father's paintings without permission.The 'Goodfellas' star was furious when Salander-O'Reilly Galleries auctioned 12 works by Robert De Niro Sr. to help pay off a $5 million debt.The Oscar-winning actor's publicist Stan Rosenfield claims the paintings were "entrusted" to the Manhattan gallery but instead of selling them on his behalf, Salander gave them to Benucci S.r.l, which owns art houses in Rome, as part of a debt repayment plan.De Niro has now hired international law firm Willkie, Farr and Gallagher to fight his battle.A spokesman for the firm said: "Based on documents that have been provided to us, it appears that in June of 2007, Salander O'Reilly Galleries attempted to settle $5 million in debt that it owed to Benucci by delivering over 50 paintings to Benucci, including 12 paintings of Robert De Niro Sr. owned by his son."De Niro Sr. was a well regarded post-war artist whose work was often displayed alongside such contemporaries as William de Kooning and Franz Kline and exhibited in museums around the country.He was awarded a prestigious Guggenheim Fellowship in 1968 and eventually died of cancer in 1993 the age of 71.