Yes, it's gonna be a problem. The IRS gets copies of all W-2's and will discover that you understated your income.
ONLY AFTER the IRS has processed your income tax return and you've received your refund - assuming the IRS doesn't catch the error - then you need to amend your income tax return.
This FAQ
https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed
will explain the process. You can't e-file an amended income tax return, you must mail it in.
Tom Young
