Ravensdown Fertiliser says it is working to stave off possible action against the cargo ship Federal Crimson, headed to the Ports of Napier, Lyttelton and then on to Dunedin.
The ship is carrying 51,000 tonnes of phosphate rock sourced in Western Sahara, and advocacy group Take Em Down Otautahi has pledged a "peaceful blockade" of the ship.
It is due to arrive in Napier on December 1, departing for Lyttelton on December 5.
The planned action is supported by local maritime unions, following last month's resolution by the international Council of Trade Unions condemning Morocco's illegal occupation of Western Sahara and to halt importation of phosphates from the area into New Zealand.
Rail and Maritime Transport Union South Island organiser John Kerr said the union made a request to Ravensdown for its members to board the vessel and deliver a letter of protest, but was declined.