The Montgomery County school system will need to significantly increase its contributions to employee pension plans over the next two to three years, according to new findings by the County Council’s Office of Legislative Oversight.

The increase — necessary in fiscal 2014 and 2015, which begin on July 1, 2013 — could be greater than 17 percent, according to the report, despite a 2 percent increase this year in employee contributions to the plan and reduced pension benefits for new hires.