The employer submits the W-2C and SS gets that. You do not have to notify them but you can request a transcript of you employment history to be sure that they applied it. Since box 3 & 4 do not affect your tax return (unless they exceed the maximum amount for the year) then there is nothing for you to do.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
