A union that represents hospitality workers must face accusations that it harassed a casino’s customers in a bid to prevail in a labor dispute, a federal judge held Monday.In a written opinion, U.S. District Judge Manish S. Shah declined to dismiss claims by Ameristar Casino East Chicago LLC that Unite Here Local 1 engaged in improper secondary boycotts.The National Labor Relations Act bars unions from targeting neutral third parties — including a business’ customers and vendors — in order to force …