Police have issued orders threatening protesters with jail and fines if they get too close to survey ships looking for deep sea oil off the coast of the East Cape.
Oil giant Petrobras has been doing seismic testing between 12 and 200 nautical miles off the Cape for a week.
That work has been hindered by Greenpeace protesters who positioned themselves in front of its ships to prevent them from working at the weekend.
Superintendent Barry Taylor said police officers on Navy rigid hull inflatable boats visited the protest fleet this afternoon.
Skippers were served notices requiring them to get no closer than 250m from the bow and stern and 200m from the port and starboard sides of the Ocean Explorer and Ocean Pioneer, he said.
Breaking the order could see protesters issued a $10,000 fine or imprisoned for up to a year under the Maritime Transport Act 1994.
"The notices were served to ensure the safety of people and property are not endangered," Mr Taylor said.
"We've assured all parties that the safety of individuals is a top priority. We also want to ensure that the lawful rights to protest and for companies to go about their lawful business are understood and respected."
He said police would continue to talk with Greenpeace and the protest flotilla.
Prime Minister John Key earlier said he was concerned at protesters stopping legal exploration work.
He had received an opinion from Crown Law that the police did have jurisdiction to uphold New Zealand law in the Exclusive Economic Zone (EEZ) which lies from 12 to 200 nautical miles offshore.
"My expectations are that the police would balance the rights of people to peacefully protest also with the rights of the company to carry out the seismic activity in Raukumara Basin that we granted them as a Government.
"How they balance those rights on the high seas is clearly an operational matter for police."
Maori Party MP for Waiariki Te Ururoa Flavell compared sending the navy to monitor the protests to Libyan dictator Muammar Gaddafi's military intervention against his people in a statement this afternoon.
"We aren't Libya so we shouldn't be using our military against our own people - it is totally over the top for the Government to be using Navy resources in this way."
He said some of the protest action could have been averted if local iwi Te Whanau A Apanui and Ngati Porou had been consulted at marae along their coast about the oil exploration work.
"We expressed our disappointment at those iwi being left out of the process in June last year, and we reiterate that again now.
"To give the people of this country confidence, the government must put the permit on hold until that consultation has happened."
Green Party MP Gareth Hughes has also criticised the Government's actions - saying they show it is more interested in protecting the rights of a foreign oil company than stopping whaling in the Southern Ocean.
"I guess it shows their priorities - they're happy to stand on the sidelines over whaling but then explore any options possible to protect foreign interests," he said.
Hughes said last year he repeatedly asked questions in the House over sending a vessel to the Southern Ocean to observe tensions between whaling vessels and protest ships, but the Government refused.
The protest flotilla is supported by East Cape iwi Te Whanau a Apanui, which says the company had no right to be in the waters that lie east of their tribal lands.
"This is not a protest," iwi spokesman Rikirangi Gage said. "This is an act of defence of our ancestral lands and waters that have sustained us for generations."
Petrobras executives were reportedly reduced to tears after meeting with East Coast locals opposed to their work.
WHO'S IN CHARGE
* Petrobras is searching for oil and gas in New Zealand's exclusive economic zone - from 12 to 200 nautical miles offshore.
* Protesters are blocking the work.
* Government has asked Crown Law to clarify legal options in that zone, including whether the Navy could be called in.
* Police say their powers outside the 12-mile territorial limit are the same as under New Zealand law - but are also exploring legal options.
* Protesters say the search is illegal.