When you file a joint federal income tax return with your spouse, you may be held liable for the lies or omissions of your spouse, even though you had zero knowledge of them. That could end up costing you a pretty penny, because the IRS can go after either spouse to collect a tax deficiency based on the principle of joint and several liability.

Strategy: If this happens to you, request “innocent spouse” relief from the IRS. Such a request is often made after a separation or divorce. In essence, you’re absolved of liability caused by your spouse or former spouse if you qualify as an innocent spouse.

But innocent spouse relief isn’t automatic. And the IRS strictly enforces the rules in this area.

Here’s the whole story: Generally, married taxpayers benefit overall by filing a joint tax return on the federal level, especially if one spouse earns significantly more than the other. Filing jointly may also help the couple maximize certain income tax deductions and credits. But there’s a catch: Each spouse is jointly and severally responsible for any tax, interest and penalties attributable to the joint return. This liability continues to apply even after a couple divorces. In other words, the IRS can try to collect the full amount due from one spouse, even if the other spouse earned all the income reported on the joint return and even if the other spouse was the one guilty of errors or omissions. However, under the innocent spouse rule, you can escape liability, despite having signed a joint return. To qualify, the following requirements must be met:

• You have filed a joint return that has an understatement of tax.

• The understatement of tax is due to erroneous items of your spouse.

• You can establish that, at the time you signed the joint return, you did not know—or have reason to know—that there was an understatement of tax.

• Taking into account all of the facts and circumstances, it would be unfair to hold you liable for the understatement.

• You and your spouse (or former spouse) have not transferred property to one another as part of a fraudulent scheme to defraud the IRS or another third party.

For this purpose, “erroneous items” are defined as any deduction, credit or tax basis incorrectly stated on the return, as well as any income not reported on the return.

Tip: The best approach is to carefully examine any joint tax return before signing it.