TAX_IDENTIFIER is a 100 alphanumeric field that can display one of two things, depending on which function the field pertains to.

In the functions IPUTP or IPRLUS, a tax identifier is also known as a State Tax Parameter which 'identifies' a state's tax parameters used to provide filing information as supplied by the client or employee to calculate the taxes. These parameters often simulate information requested on the withholding certificate of the state. For example, FILINGSTATUS is a common Miscellaneous Tax Identifier.

In functions such as IPPH and IPUTR a Tax identifier is used to indicate a tax type by location code. For example, 34-000-0000-SIT-000-Res-Reg. These provide a mechanism to allocate a tax rate/tax amount to a specific tax jurisdiction. The first two digits in the Tax Identifier indicate the FIPS code of the state. The second segment indicates the county, if the tax rate is specific to a county. The third segment indicates the City's Feature id, if the tax rate is specific to a City otherwise it will be zeros. The fourth segment indicates the type of tax for example, SIT for State Income Tax or ER_SUTA for Employer State Unemployment Tax. A list of Tax Identifiers can be found by state in the IPUTR form.