How do you fight the IRS for refund that has been held for spouses back taxes?

Go to the IRS gov web site and use the search box for form 8379 go to page 2.

Form 8379 is filed by one spouse (the injured spouse) on a jointly filed tax return when the joint overpayment was (or is expected to be) applied (offset) to a past-due obligation of the other spouse. By filing Form 8379, the injured spouse may be able to get back his or her share of the joint refund.

Are You an Injured Spouse?

You may be an injured spouse if you file a joint tax return and all or part of your portion of the overpayment was, or is expected to be, applied (offset) to your spouse's legally enforceable past-due federal tax, state income tax, child or spousal support, or a federal nontax debt, such as a student loan.

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