When consent is required
The default under 301.7216-3(a)(1) is that a preparer may not disclose or use a taxpayer’s return information before obtaining written consent, and the consent must be knowing and voluntary. The exceptions are in 301.7216-2.
For outsourcing, the key exception is 301.7216-2(d)(1): disclosure to another preparer located in the United States for preparation or auxiliary services, where the second preparer does not make substantive determinations. Disclosure to a preparer outside the United States, or for substantive determinations, needs consent first.

