New withholding tables may reduce the amount of federal income tax withheld from your wages. Employees paid semimonthly will see these changes effective with the March 31 paycheck. Employees paid biweekly will see the changes effective with the April 3 paycheck.
According to the IRS, "the new tables, prescribed by the Department of the Treasury, reflect the Making Work Pay credit and other changes resulting from the American Recovery and Reinvestment Act of 2009."
You do not have to submit a Form W-4, Employee's Withholding Allowance Certificate, to get the automatic withholding change. If you do not want to have your withholding reduced, you may want to file a new Form W-4 with the Payroll Office. You may claim fewer withholding allowances on line 5 or request additional amounts be wittheld on line 6
For additional help, see IRS Publication 919 ("How Do I Adjust My Tax Withholding?") or visit the IRS website at www.irs.gov and use the Withholding Calculator.
https://www.ithaca.edu/intercom/article.php/20090325094153692