The protestors who attacked the Waihopai spy base say they are trying to stop New Zealand from becoming a terrorist target.

Three protestors have been arrested over the attack, which left one of the base's plastic domes deflated and has been described by Prime Minister Helen Clark as "senseless". The accused men; Adrian Leason, Sam Land and Dominican Friar Father Peter Murnane, are due to appear in the Blenheim District Court this afternoon.

Their lawyer Moana Cole believes they will at the very least be charged with criminal damage. She says police may lay further charges but have given no indication of whether they will oppose bail.

Spokesman for the protest group Manu Caddie says they are concerned that the base is being used to help the US war on terror. He says the protestors were "following through on the gospel and being faithful to that when it comes to peacemaking".

Mr Caddie says the protestors decided to act after reading a book by Nicky Hager.