The Vanuatu opposition claims the government bowed to pressure from China despite fears foot and mouth disease could be introduced.
The Chinese company rebuilding Bauefield Airport was stopped last month from unloading metal for fear of contamination.
But machinery and equipment on the vessel has now been brought ashore.
Our correspondent in Vanuatu reported this equipment may have come in contact with contaminated metal.
The opposition said the unloading happened despite the concerns of quarantine officials and farmers.
It said agriculture was a key industry for Vanuatu and to ignore regulations and offload potentially contaminated goods was a slap in the face for the sector.
Opposition leader, Ishmael Kalsakau, said his MPs recognised the relationship with China but said Vanuatu, as a sovereign nation, cannot allow foreigners to ignore safeguards.