As USCG highlights, Section 2  of the EO  specifically states,

“No vessel in which a foreign person has an interest that has called at a port in North Korea within the previous 180 days, and no vessel in which a foreign person has an interest that has engaged in a ship-to-ship transfer with such a vessel within the previous 180 days, may call at a port in the United States.”

USCG clarifies that the prohibition applies, except to the extent provided by statutes, or in regulations, orders, directives, or licenses that may be issued pursuant to this order, and notwithstanding any contract entered into or any license or permit granted before the effective date of this order.

The Department of Treasury has issued General License Number 10 – Calling of Certain Vessels and Landing of Certain Aircraft Authorized (September 21, 2017). Visit the Office of Foreign Assets Control (OFAC) website for more information. 

USCG advises shipping agents and other maritime stakeholders that have identified a vessel in transit that falls into one of the categories listed above are advised to contact their local Captain of the Port (COTP) to avoid potential delays or disruption to commerce.