Form 8594 must also be filed if the purchaser or seller is amending an original or a previously filed supplemental Form. 8594 because of an increase or decrease.Form 8594 is a tax document required in certain business sales where the buyer acquires assets rather than stock or equity. Who Must File Form 8594? Both the seller and purchaser of a group of assets that make up a trade or business need to file Form 8594. If you are calling from outside of the 48 contiguous states, please call 1-916-445-6362 or complete our online form to reach our Customer Service Center. Line 1: Enter the name, address, and Tax Identification Number (TIN) of the other party (either the purchaser or seller). Attn: Elias Vamvakas.