Significant problems can arise for taxpayers if their ITIN and SSN are mismatched on their federal income tax returns. 

Due to this, tax preparers should take extra care to confirm that the correct taxpayer identification number is reported on the tax return. This will avoid mismatch errors and correspondence from the IRS, and if filing the return electronically, will also prevent rejection of the return. IRS suggests confirming the number by seeing social security cards, ITIN letters, etc. The IRS requires taxpayers filing tax returns using an Individual Taxpayer Identification Number (ITIN) who are reporting wages paid to show the Social Security Number (SSN) under which the wages were earned. This creates an identification number (ITIN/SSN) mismatch. Taxpayers should use their correct ITIN as the number on the face of Form 1040, but when inputting Form W-2 information for electronic filing purposes, the taxpayer’s SSN exactly as shown on the W-2 issued by the employer should be entered. (IRS Pub. 1345, page 10, rev. 10-2024)