Last month, President Obama signed into law a two-percent reduction in payroll tax for workers who pay into Social Security. The deduction will fall from 6.2 percent to 4.2 percent. OASDI stands for Old Age, Survivors and Disability Insurance. For employees paid monthly, the OASDI reduction will be reflected on Feb. 1 paychecks and will include the adjustment for January 2011. For employees paid biweekly, the change will be reflected on Jan 14 paychecks.