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Your prenuptial agreement cannot bind the IRS. However, you can use it as a part of an argument that you are entitled to innocent spouse relief. I will get you a link to the form for this application and return momentarily. In the future, to avoid this problem, you may wish to file separate tax returns.
Here is a brief piece from the IRS. It contains information about form 8857 (application for innocent spouse relief). Please remember that, unless the IRS was a party to your prenuptial agreement, they are not obligated to separate your tax obligations.
Topic 205 - Innocent Spouse Relief (Including Separation of Liability and Equitable Relief)
Many married taxpayers choose to file a joint tax return because of certain benefits this filing status allows. Both taxpayers are jointly and severally liable for the tax and any additions to tax, interest, or penalties that arise as a result of the joint return even if they later divorce. Joint and several liability means that each taxpayer is legally responsible for the entire liability. Thus, both spouses are generally held responsible for all the tax due even if one spouse earned all the income or claimed improper deductions or credits. This is also true even if a divorce decree states that a former spouse will be responsible for any amounts due on previously filed joint returns. In some cases, however, a spouse can get relief from joint and several liability.
There are three types of relief from joint and several liability for spouses who filed joint returns:
NOTE: You must request relief no later than 2 years after the date the IRS first attempted to collect the tax from you, regardless of the type of relief you are seeking. Not all IRS attempts to collect the tax from you will trigger the two year period for filing a request for relief. Collection activities that may start the two year period are:
You must meet all of the following conditions to qualify for "innocent spouse relief":
To qualify for "separation of liability relief" you must have filed a joint return and must meet one of the following requirements at the time you request relief:
If, at the time you signed the joint return, you had actual knowledge of the item that gave rise to the understatement of tax, you may not qualify for separation of liability relief.
You may qualify for "equitable relief" if you do not qualify for innocent spouse relief or separation of liability relief. Equitable relief is available for additional tax owed because of a reporting error (an understatement) or you properly reported the tax on your return, but you did not pay it (an underpayment). To qualify for equitable relief you must establish, under all the facts and circumstances, that it would be unfair to hold you liable for the understatement or underpayment of tax. In addition, you must meet other requirements listed in Publication 971, Innocent Spouse Relief.
Form 8857 (PDF), Request for Innocent Spouse Relief, or a written statement containing the same information required on Form 8857, which is signed under penalties of perjury, must be filed in order to request innocent spouse relief, separation of liability relief, or equitable relief. You may also refer to Publication 971, Innocent Spouse Relief, for more information. If you request relief from joint liability, the IRS is required to notify the spouse with whom you filed the joint return of your request and allow him or her to provide information for consideration regarding your claim. To learn more about innocent spouse relief, you can use the Innocent Spouse Tax Relief Eligibility Explorer at www.irs.gov. Click on "Individuals," "Tax Information for Innocent Spouses," and "Explore if you are an Eligible Innocent Spouse."
If you lived in a community property state and filed as "married filing separate" rather than "married filing jointly", you might still qualify for relief. Community property states are Arizona, California, Idaho, Louisiana, Nevada, New Mexico, Texas, Washington, and Wisconsin. Refer to Publication 971 for more details.
Relief from joint and several liability should not be confused with an injured spouse claim. You are an "injured spouse" if you file a joint return and all or part of your share of the refund was, or will be, applied against the separate past-due Federal tax, state tax, child support, or Federal non-tax debt (such as a student loan) of your spouse with whom you filed the joint return. If you are an injured spouse, you may be entitled to recoup your share of the refund. For more information, obtain Form 8379 (PDF), Injured Spouse Allocation, or refer to Topic 203, Failure to Pay Child Support, Federal Non-Tax and State Income Tax Obligations.