All sanctions imposed by any government are effectively nationwide legally imposed boycotts.

Sanctions against Russia for example are generally things like : we will not buy your oil, we will not allow our companies to sell products to you, etc. etc.

Same thing goes for sanctions against individuals, they make it illegal for any US based entities to have certain scopes of dealings with the target. Some sanctions go further and also refuse to deal with entities who deal with the target.

Therefore, depending on what sanctions have been imposed, they may have just made it illegal for them to have a visa or MasterCard, use any Microsoft or Google or apple software or services, etc. etc. etc.

• It’s the other way around actually. Illegal for Visa/MasterCard or Microsoft or Google or apple, etc. to allow them to use their services.