The Service Employees International Union, the country's fastest growing union, is trying to organize more than fifteen hundred twin cities school bus drivers. According to an official with the National Labor relations board in Minneapolis , it would be one of the largest Minnesota union votes in recent memory. The union petitioned the board for a vote yesterday, the same day that Eden Prairie school bus drivers who already are represented by the union ratified a contract with a double digit increase in wages and benefits. As Minnesota Public Radio's Bill Catlin reports, the union's president says bus drivers represent a growth opportunity.