Italian unions on Monday refused to load electricity generators onto a Saudi ship carrying weapons that could be used in the war in Yemen.
The Saudi-flagged Bahri Yanbu docked at the Italian port of Genoa on Monday, despite protests by harbour workers.
It is scheduled to load further cargo before departing for the Saudi port of Jeddah late on Monday, according to the Italian news agency ANSA.
Port workers protesting the alleged arms shipment unsuccessfully tried to prevent the ship's arrival, and hoisted a banner reading "Stop the trafficking of arms, war to war."
ANSA says union and port officials were in talks on the cargo to be loaded.
The 50,000-tonne ship has already called at several European ports, reportedly to pick up weaponry. French officials said a scheduled loading of arms at Le Havre was cancelled following protests by activists.
The issue of Saudi arms sales divides European governments, with French President Macron defending such sales as part of "the fight against terrorism".
Germany however suspended arms sales to Riyadh after the killing last year of Saudi dissident Jamal Khashoggi in Istanbul, posing a problem for European partners as this could affect joint weapon production.
The Yemen war has cost tens of thousands of lives since it broke out in 2014 and escalated with the Saudi-led coalition intervention in 2015.
The war has led to what the United Nations describes as the world's worst humanitarian crisis, with 3.3 million people still displaced and 24.1 million - more than two-thirds of the population - in need of aid.