Tax rules designed to protect married taxpayers who file joint returns from being held responsible for taxes due to erroneous actions by their spouses—such as failing to report income or claiming unsubstantiated deductions. Basically, if you can show that you didn’t know and didn’t have reason to know about error that resulted in the underpayment of tax on the joint return, you can be relieved of responsibility for that underpayment. You have two years from the time the IRS begins trying to collect the underpayment to petition for innocent spouse relief.