Greenpeace has opened its case against the Environmental Protection Agency and Texan oil giant Anadarko in the High Court at Wellington.
The organisation alleges the Environmental Protection Agency (EPA) failed in its role to properly consider whether permission should have been granted to Anadarko to drill for oil in the Taranaki Basin.
Anadarko, which began drilling about 185km off the coast of Raglan about two weeks ago, are second respondents in the case.
Today's case is the beginning of a judicial review sought by Greenpeace into the process in which the EPA granted the company permission to undertake oil drilling.
During his opening today, Greenpeace lawyer Isaac Hikaka submitted key documents and sections of reports stating possible impacts and emergency response plans to a possible oil spill were not considered by the EPA before it granted Anadarko permission to drill.
Included in the "gap" in documents were a comprehensive and detailed impact assessment, emergency oil spill response plan and appendices referred in documents considered by the EPA during the process.
Without considering these documents and reports, the EPA was unable to fulfil its role, and erred in the law, Mr Hikaka said.
It also meant the public did not have a complete understanding of the issue during the consultation process, he said.
Mr Hikaka also told the court Maritime New Zealand, in its role to uphold marine protection laws, had received the full package of documents.
"The EPA and therefore the public through the consent process needs the same information [as Maritime New Zealand] on what the impact on the environment and existing interests will be," he said.
The case, which is before Justice Alan MacKenzie, continues.