GROSS_WAGES is a field which will display the pre-tax wages used to calculate the tax. The Pre-Tax wages are determined by the pay element associated to the Pre-Tax Wages Pay Component in IPPC for the particular tax type. There are Pre-Tax Wage pay components used for most of the tax identifiers, for example for the 06-000-0000-SIT-000-Res-Reg tax identifier UPCALC will derive the wages from PC Usage 6651 Pre-State Earnings - Reg Tax Table Method (PPE).
For more information on which Pre-Tax Wage Pay Components are available please see US PC USAGES
