Per IRS Instructions for Schedule M-3 (Form 1065) Net Income (Loss) Reconciliation for Certain Partnerships, on page 1:
Any entity that files Form 1065 must file Schedule M-3 (Form 1065) if any of the following is true.
A common trust fund or foreign partnership must file Schedule M-3 if it meets any of the tests discussed above.
Note. All references to a U.S. partnership in these instructions refer to any entity required to file Schedule M-3 (Form 1065), where appropriate.
Partnerships not required to file Schedule M-3 may voluntarily file Schedule M-3.
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the webpage or document at the time it is accessed.