Individuals and companies who are sanctioned by OFAC completely lose access to the banking and financial systems, inside and outside U.S. This is because majority of international banking transactions is channeled through New York and is done using US dollars.

The inclusion of an individual in the list may also have collateral consequences, such as being stopped for secondary inspection at immigration and customs entry points into the U.S., and being placed on U.S. “NO-FLY” lists. The negative consequences may also affect the family members of the persons included in the lists.

The impact of the OFAC sanctions goes beyond the U.S. borders. Any “U.S. person” (US company), irrespective of his/her country of residence, must comply with the sanctions. Moreover, many financial institutions who are not U.S. persons prefer not to engage in transactions with designated individuals and corporations, despite lacking a legal duty to do so.

Any U.S. person (or US company) who engages in transactions in violation of the OFAC regulation may face fines of up to $250.000 or of an amount equal to the value of the illegal transaction. This is a strict liability infraction, which means that OFAC may also penalize non-intentional transactions. Furthermore, the Department of Justice may also bring criminal actions based on the violation of OFAC sanctions. An intentional violation of OFAC prohibition may result in up to 30 years of imprisonment.

Financial institutions and companies must design, implement, and constantly update their compliance programs to prevent transactions that, directly or indirectly, involve designated individuals or prohibited transactions under the executive orders. Additionally, these entities must train their employees, compliance officers, and directors to prevent their engagement in the same forbidden transactions.

OFAC sanctions typically involve freezing of assets, and the prohibition to engage in transactions involving property and interests in property of a listed individual or entity. Thus, the sanctions cover the exchange of assets (i.e. exports and imports) and services (i.e. financial services). Additionally, sanctions generally prohibit any activity that facilitates, in any way, transactions with the designated individual or company.

Reference:
https://www.hg.org/legal-articles/ofac-list-in-the-usa-sanctions-and-consequences-47906