Legitimate protesters could be charged as terrorists under new legislation unless changes are made, the NZ Law Society says.
New Zealand's history of protest at sea, including against the visit of US nuclear vessels during the 1970s and 1980s, was cited during submissions on the law change today.
Parliament is considering legislation that will bring New Zealand up to date with current international rules about maritime security.
It will create new offences related to maritime terrorism and maritime boarding.
But there are concerns that the law change could be used to stifle protest at sea because the definition of what is terrorism is too broad.
Jonathan Orpin of the NZ Law Society appeared before Parliament's Foreign Affairs, Defence and Trade committee today and argued for the terrorism definition to be tightened.
The current definition is to carry out or to threaten acts with the purpose of intimidating a population or to compel a government or organisation.
Orpin submitted that should be changed to match the terrorism definition in other legislation - including an intention to induce terror in a civilian population, or to unduly compel or force a government or organisation.
The Law Society also wants the legislation to state that the fact a person engages in any protest, advocacy or dissent is not, by itself, sufficient to infer terrorism.
Finally, the society recommends that the wording of the law be changed to only capture those who use a ship in a manner that intends to cause death, serious injury or damage.
"If you had flotilla vessels out in a harbour protesting a visiting ship...if there are lots of ships present...it is conceivable that a genuine accident occurs," Orpin said.
"No one is ramming a vessel but they are in close contact to make a point to wave banners, and someone dies or is seriously injured...that, on its face, would appear to come within the [terrorism] section. And the society doubts very much that is the intention of Parliament."
National and Hamilton East MP David Bennett responded, saying if someone puts their boat in a position where another vessel could run into it, that was intent.
"I disagree with you that you are just running around and it sort of happens. It's like walking across the motorway, you put yourself in that position and something is going to happen.
"This is a foreign power's vessel - it is a military vessel - you are getting in the way of it. It is a terrorist act in a foreign country, isn't it. That could be the argument."
The Human Rights Lawyers Association and Friends of the Earth NZ also submitted that the current terrorism definition was too broad, and the vast majority of protesters who commit illegal acts should be excluded.
The Maritime Crimes Amendment Bill passed its first reading with support from all parties. Labour and the Greens have indicated they would require amendments to continue their support.