Local 770 of the United Food & Commercial Workers International Union on Wednesday said that union members working for the El Super supermarket chain have voted to authorize contract negotiators to call a strike if negotiations break down. The union’s contract with the Paramount-based bargain chain, which has supermarkets in California, Arizona and Nevada, expired in September. Mexican supermarket giant Grupo Comercial Chedraui owns more than 80 percent of El Super, which opened in Southern California in 1997. It operates 14 stores in Los Angeles County, including one each in North Hollywood, Arleta, Panorama City and San Fernando, according to its web site. The union said, which held the strike authorization vote on Friday, said it has complained to the National Labor Relations Board about what it described as a variety of harassment of workers and anti-union activities by El Super management in recent months. An El Super representative did not return calls by publication time.