If you file a joint income tax return with your spouse, you are considered "jointly and severally" liable for the payment of all taxes owed. The IRS can come after either you or your spouse for the entire amount of tax due, plus any penalties and interest due.
The law has “innocent spouse” rules that may limit an individual’s responsibility for unpaid taxes resulting from filing a joint return. If the “innocent spouse” can establish that he or she did not know, or have reason to know, that there was an understatement of tax when signing the joint return, relief can be requested. Under previous rules, this relief had to be requested within two years after collection proceedings were initiated by the IRS.
In a recent ruling, the IRS has decided to eliminate the two-year time limit for requesting innocent spouse status under the “equitable relief” provision in the law.