Nearly every union staff member at a charter school chain voted Wednesday to authorize a strike if negotiations remain stalled. Ninety-nine percent of the staff at the four Aspira schools on the Northwest Side voted in favor of the strike. If the staff does walk, it would be the first charter school teacher strike in history. The approximately 100 Aspira Charter School staff have been in negotiations since May. Union president Marines Martinez said no strike date has been set and stressed that Aspira employees do not want to walk out.