"The law ... was intended to cut an estimated $45 billion unfunded liability in the Michigan Public School Employees Retirement System by more than $15 billion.... [S]chool employees hired before 1990 -- who were paying nothing toward retirement -- must contribute 4% of their pay or have their benefits cut. Those hired from 1990 to June 2010 must pay 7% to keep their pensions intact. Previously, they paid 3% to 6.4%. Those hired since the middle of 2010 are in a 401(k)-type pension plan and aren't affected by the law."