That's because the IRS finds that married couples who filed their tax returns jointly are separately and jointly responsible for each other's tax liability. This means if the IRS can't collect taxes from your spouse, but they may attempt to collect taxes from you. The IRS does this because it reasons that you were in a position to know about you spouse's underreporting of income, and that you likely benefited from your spouse's misdeeds.

However, the IRS recognizes there are exceptions to these assumptions, and has created "the innocent spouse rule" to exempt qualifying taxpayers from their spouse's misdeeds. If you can demonstrate that your spouse was truly uninvolved and did not benefit from their spouses tax misstatement, you can alleviate your IRS problem.

In order to do so, you must prove three things:
1. You must prove that you were unaware of the understated income.
2. You had no reason to be aware of the erroneous tax claim.
3. You did not benefit from your spouse's tax misdeeds.

To prove that you are not benefiting from your spouse's tax evasion, you must be able to show that your lifestyle is commensurate with the income listed on your return. In other words, if your tax return states that your joint income is $30,000, but you live in a lavish mansion and drive a luxury sports car, the IRS may find that you benefited from your spouse's misstatement and therefore were aware (or should have been aware) that your spouse did not claim.

In order to demonstrate that you did not benefit from your spouse's tax misdeeds, you will have to be prepared to demonstrate that your lifestyle (the car you drive, where you live, etc.) is in keeping with the income you and your spouse reported on your tax return.

If you think you qualify for the innocent spouse rule, complete Form 8857, “Request for Innocent Spouse Relief," which can be downloaded from the IRS's website. A qualified tax pro may be able to assist you in completing the form and help you including the proper substantiation.