As early voting in Tennessee gets underway, Knoxville voters will cast ballots that could change the city charter. At issue: the pension plan for city workers. Knoxville Mayor Madeline Rogero has proposed what she calls a "hybrid" pension plan. It would apply to any employee hired after January 1, 2013, and would close the current pension plan. Changes will include a rise in retirement age and an increase in the pension vesting period (from 5 years to 10 years). The new plan would also put limits on defined benefits, or those benefits guaranteed by the city.