On May 8, 2018, the U.S. President announced his decision to cease the United States' participation in the Joint Comprehensive Plan of Action (JCPOA), and to begin re-imposing the U.S. nuclear-related sanctions that were lifted to effectuate the JCPOA sanctions relief, following a wind-down period.
Withdraw from the nuclear deal
The president poured scorn on the "disastrous" 2015 accord, describing it as an "embarrassment" to the United States that does nothing to contain Iran's nuclear ambitions.
I am announcing today that the United States will withdraw from the Iran nuclear deal.
Signatures on JAPOA 
Come back into full effect
The State Department plans to take appropriate action to keep necessary statutory sanctions waivers in place for the duration of the relevant wind-down periods.
Consistent with the President's guidance, Departments and Agencies will begin the process of implementing 90-day and 180-day wind-down periods for activities involving Iran that were consistent with the U.S. sanctions relief specified in the JCPOA.
The sanctioned industries include transport, energy, automobile and finance.
And At the end of the 90-day and 180-day wind-down periods, the applicable sanctions will come back into full effect.
Official announcement link 
https://www.treasury.gov/resource-center/sanctions/Programs/pages/iran.aspx
Negative impacts
Number of Shipping route headed to Iran decreases recently due to Ramadan is drawing near. The most direct impact on the shipping market might be that shipping space in Bandar Abbas will be over-demanded, along with the increasing transport costs.
Increasing difficulties on transportation between China and Iran will be the most direct influence on foreign trade industry. Previously, because of sanction, many shipping companies stopped accepting cargoes shipped to Iran, and stopped calling ports in Iran area.
No more dollars!
Iranian government institutions had announced before that they would report foreign currency amounts in Euros rather than US Dollars, as part of the country’s effort to reduce its reliance on the American currency.
Referrence article: 
Risk Warning? Euro will Replace Dollar in Iran!
Therefore, shippers are reminded that pay close attention to the follow-up situation and be careful about risks when arrange shipping schedule!
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Ref | U.S. Department of the Treasury
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