31 CFR 543.405 - Provision of services.
(a) The prohibitions on transactions involving blocked property contained in § 543.201 apply to services performed in the United States or by U.S. persons, wherever located, including by an overseas branch of an entity located in the United States:
(b) Example. U.S. persons may not, except as authorized by or pursuant to this part, provide legal, accounting, financial, brokering, freight forwarding, transportation, public relations, or other services to a person whose property and interests in property are blocked pursuant to § 543.201(a).
See §§ 543.507 and 543.508 on licensing policy with regard to the provision of certain legal and medical services.