Greenpeace has asked the Wellington High Court for an urgent hearing into its application for a judicial review of a decision to allow exploratory drilling for oil in deep sea off the Raglan coast.
Texan oil company Anadarko's Noble Bob Douglas began drilling at 2.30am on Tuesday, not long before a flotilla of protest boats decided to return to port.
Greenpeace says that the six boats succeeded in making a point and it was now time to focus on the next stage.
The organisation says it believes that New Zealand's Environmental Protection Authority made an error in law by allowing the American company to go ahead without looking at key documents.
Lawyer Duncan Curry said Greenpeace believes the assessment is lacking in a number of areas, such as contingency plans in the case of an emergency spill. He said any legal argument would look at the state of the documents provided and whether Anadarko has complied with the legislation.
Mr Curry said Greenpeace believes that the company hasn't, and the oil spill issue goes to the heart of its concerns. He said a simple question for the court is also whether the Environmental Protection Authority viewed all relevant documents before granting permission to drill.
One protest vessel, Vega, spent the past few days within a 500-metre safety zone, while other yachts had been just outside the area while the drilling ship prepared to start work. Greenpeace executive director Bunny McDiamid said despite returning to shore, crews would continue the campaign for a cleaner New Zealand.
Anadarko corporate affairs manager Alan Seay said the Noble Bob Douglas would drill for 70 days when it expects to reach its target depth and delayed work because of the time taken getting vital equipment from the shore.
Mr Seay said the Vega was a distraction, as the company had to devote extra staff from the drilling operation to keep an eye on it in the safety zone, and Anadarko would let any court action take its course.
The Green Party's energy spokesperson, Gareth Hughes said he believes Greenpeace has a good case and Anadarko should stop work in the meantime.
"I think what we see in this legal avenue is questions around the process of the application. And given we've got such severe consequences of a spill if it was to occur, I think Anadarko should delay."
Mr Hughes described the process around granting Anadarko permission to drill as an utter shambles.
However, Prime Minister John Key said the Environmental Protection Authority is confident it made the right decision.
"I don't see any particular reason why they (Anadarko) should stop. This will just be another stunt by the Greens and by Greenpeace. If they believe that they've got a legal case, they should go and take it to court and test it."