This selection associates your payments with a “signatory,” a party signed to a union agreement. Different agreements stipulate specific rates for union Health & Retirement contributions. They also invoke different templates for calculating earnings and fees. Most users will want to select Standard Eljin from the dropdown. But if you’re paying narrators you’ve engaged through ACX, choose ACX US. For more on ACX business logic, see the note to “What does the Reverse calculation/flat-fee checkbox do?”