Signed into law by President Reagan, the Federal Employees' Retirement System Act applies to employees hired after December 31, 1983. This is a departure from the Civil Service system and requires employees to participate in Social Security. It also permits FERS participants to contribute up to 10 percent of their earnings, on a tax-deferred basis, to a thrift savings plan - similar to a 4011(k) - with partial matching by the Government.