NEWPORT BEACH, Calif.—Two local museum directors are not happy that the Orange County Museum of Art quietly sold 18 of its 20 California Impressionist paintings to an undisclosed private collector in March. It’s the latest case in what has become a sensitive issue lately for museums, as several economically pressed nonprofit institutions have sold or resolved to sell works to pay general expenses.

OCMA Director Dennis Szakacs said the paintings from the early 1900s were sold for $963,000 to a Laguna Beach purchaser, noting that the decision was based on “the desirability of keeping these paintings with a local collector.” The money will be used only to buy art for the collection, which now focuses on post-1950s works, he added. Still, the directors at the Laguna Art Museum and the Irvine Museum say the transaction’s secrecy violated the public interest by preventing them from bidding to keep the works in collections open to the public. Both directors say that the works, which are in the "pleine air" style, are of a genre important to their museums and that if they’d known the paintings were for sale, they would have sought donors to bankroll bids.