*The union representing on-air employees at WLUP-FM (97.9) is in a fight for its life. Staffers at the Emmis Communications classic rocker will decide next month whether to drop the American Federation of Television and Radio Artists as their representative.The decertification vote, to be supervised by the National Labor Relations Board, was prompted by a petition from new staffers who questioned the need for a union contract and objected to dues and fees.In a letter to employees, Marv Nyren, vice president and general manager of the Loop, wrote: "We believe that once you have all the information, you will decide that the union is really not in your best interest or in the best interest of WLUP, and that you will tell that to the union by voting 'NO' on election day."Eileen Willenborg, executive director of AFTRA's Chicago local, said the station's 22 staffers covered by the contract might not be fully aware of what they'd be giving up. "We're confident that when our message is delivered, they'll understand the benefits of union protection," she said.