Diplomats from five major nations have been summoned to Parliament to be given a blunt message to reduce or eliminate their nuclear weapons.
A letter, signed by 60 MPs from all political parties, was being delivered to the diplomats representing Britain, Russia, the United States, China and France.
The letter calls for those countries, who signed the Non-Proliferation Treaty in 1970, to begin the process of nuclear disarmament now.
New Zealand Parliamentarians for Nuclear Non-Proliferation and Disarmament chair Phil Goff said the five nations had failed to honour the treaty.
The Labour MP said countries which had met their side of the bargain were becoming impatient with those which had not.
"As long as you don't meet your side of the bargain, there is a real risk that pepole will opt out of their side of the bargain, and we will see further proliferation and, in this age of terrorism, it's surely only a matter of time before a terrorist group gets their hands on a nuclear weapon and then you've got a totally world-changing situation," he said.
"That is the nightmare scenario."
Mr Goff said there were 17,000 nuclear war heads in existence - far more than was needed as a deterrent and enough to destroy the world many times over.