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. Enter your name and taxpayer identification number (TIN) at the top of the form. Then check the box for Purchaser or Seller. 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.