1. (a) Every corporation is a separate taxable entity and shall file its own report. However, a combined report covering a group of corporations engaged in a unitary business is required in certain circumstances. A combined report covering any taxpayer and another corporation or corporations is required where:

   1. (1) the capital stock requirement (as described in section 6-2.2 of this Subpart) is met; and
   2. (2) the substantial intercorporate transactions requirement set forth in section 6-2.3 of this Subpart has been met.
2. (b) Where the capital stock requirement is met and substantial intercorporate transactions are absent, a combined report covering corporations engaged in a unitary business may be required or permitted if the commissioner deems such a report necessary, because of inter-company transactions or some agreement, understanding, arrangement, or transaction, in order to properly reflect the tax liability under article 9-A of the Tax Law.
3. (c) Each corporation in the combined report must compute and show the tax which would have been required to be shown if filed on a separate basis.

Tax Law, § 211(4)