Pita is employed as an administrator for Postman Plus. Pita noticed that Box $1$ and Box $3$ amounts on the W$-2$ were different.

b Employer identification number $($EIN$)1$ Wages, tips, other compensation $2$ Federal income tax withheld

c Employer's name, address, and ZIP code $3$ Social security wages $4$ Social security tax withheld

What is a reason why the amounts in boxes $1$ and $3$ would be different?