About 100 protesters demanding jobs and better state services closed access to Umm Qasr port near the southern Iraq city of Basra on Friday, port employees said.
"They blocked the road leading into the port and trucks have no way of getting in or out. Port officials have asked us to go home," one worker told Reuters.
Basra oil officials have said four days of demonstrations, which have also taken place near major oilfields, have not impacted crude production.
"We will not stop until our demands are met," said Mohammed Jabbar, 29, an unemployed college graduate.
"If they don't create jobs and improve services such as water and electricity we will close down Basra and oil production."
Iraqi Prime Minister Haider al-Abadi was holding talks with officials in the oil-exporting city of Basra to discuss the unrest.
The harbour near Basra receives grain shipments and heavy equipment used in the oil industry.
(Reporting by Aref Mohammed; writing by Michael Georgy; editing by Jason Neely)