New Zealanders who take part in protests at sea could be treated as terrorists and face draconian punishments under proposed law changes, MPs have been told.

Photo: GREENPEACE

Submitter after submitter warned the Foreign Affairs and Defence Select Committee that, under the government's Maritime Crime Amendment Bill, acts of civil disobedience at sea - such as boarding or damaging a warship - could be classified as terrorism.

They said the bill was heavy-handed and such behaviour could be dealt with by criminal charges.

Tim Jones from the Coal Action Network said the tradition of protesting at sea was under threat.

"That it could be used in such a way as to prevent, or to seek to prevent ... or have a chilling affect on legitimate protest activity."

Feroze Brailsford, 19, told the committee New Zealand had a proud history of civil disobedience, including challenging apartheid and nuclear weapons.

"They committed criminal offences and again we validate them today, proudly enshrining them as part of out national identity.

"You may disagree ... but I believe most New Zealanders actually feel very proud, intensely proud, of the position that we took against apartheid and against nuclear weapons."

Photo: RNZ / Alexander Robertson

Government MP and committee member David Bennett said anyone who got in the way of a foreign warship was clearly a terrorist.

"This is a foreign power's vessel, a military vessel, you're getting in the way of it - so it is a terrorist act on a foreign country isn't it," he said.

Jonathan Orpin is a member of the Law Society's law reform committee.

He recommended the government amend the legislation so the definition of terrorism was the same as in the Terrorism Suppression Act, and separate it from protest action.

"The Terrorism Suppression Act appears to set a slightly higher threshold which would appear in the society's submission to be appropriate, again to try and draw a distinction between legitimate acts - protest which aren't intended to be captured - and terrorist acts."

Green Party global affairs spokesperson Kennedy Graham - who sits on the select committee - said the bill needed to be amended to make it clear that "protest, advocacy and dissent" on the seas were not terrorism.