If one of your W-2's came after you filed your taxes, when this is discovered by the IRS usually around August or September (when they have matched up the W-2's to the ones sent in by employers to the ones claimed by employees) they will send you a tax bill for that W-2. The tax could be 25-30% of the income on the W-2, so if it is for $800.00, they will send you a bill for $200-$250 dollars. You may consider contacting them and telling them about this before they catch it so it will be noted. They WILL find it. And this does not mean you will be audited.