If you owe delinquent federal taxes, IRS will withhold the balance due from your refund. If your refund exceeds the amount of your delinquent federal taxes, IRS will adjust your split refund direct deposits under the bottom-up rule discussed earlier (see What if a mistake on my return decreases the amount of my refund?)

If you also owe delinquent state income taxes, back child support, or delinquent non-tax federal debts such as student loans, etc., the Department of Treasury's Financial Management Service (FMS) will deduct the past-due amounts from the payment that appears first on the payment file received from IRS (the IRS payment file orders accounts from the lowest to the highest routing number). If the debt exceeds the payment designated for the account that appears first on the payment file, FMS will reduce the payment designated for the account that appears next, etc.

You will receive a letter explaining any adjustments IRS made to your refund amount and direct deposit(s). You will receive a separate letter from FMS explaining any offset amount, the agency receiving the payment, the address and telephone number of the agency, and amount of your refund/direct deposit that was offset. If you dispute the debt on the letter you receive from FMS, you should contact the agency shown on the notice, not IRS, since IRS has no information about the validity of the debt.

Information about your refund offsets will also be available through Where's My Refund?

Source: www.irs.gov