You can use the Office of Personnel Management’s Services Online (http://www.servicesonline.opm.gov/mainris.htm) or call (888) 767-6738 to start, change, or stop voluntary withholdings federal and state income taxes, checking and savings allotments, or make one-time or recurring allotments to other participating organizations.
When using the self-service systems, you need your claim identification number, Personal Identification Number (PIN), and Social Security Number. If you do not have a PIN, call OPM at the number above. You need a touchtone telephone to call the automated telephone service. If you do not have a touchtone telephone, you can speak to a customer service specialist.
Generally, in the middle of month, OPM authorizes payments that are due for the first business day of the following month. Therefore, if you want your change to be reflected in your next payment, you should submit your request as early as possible.