It is only a matter of time before somebody is injured or killed on a fishing trip organised by a cowboy operator, fishing guides say.
The Professional Fishing Guides Association estimates less than half of the 400-plus guides now working in the country have health and safety plans or are even paying tax.
It wants all guides to be licensed.
The group said rogue guides were putting the country's reputation as a great place to fish for trout and salmon at risk.
Spokesperson Craig Smith said it was only a matter of time before a client being led by a rogue operator was badly injured or killed.
"[Guides are] not going to tell you they're playing outside the rule book and so you can find yourself in a situation - and we've got evidence of this - of guides that aren't in our association and very near misses in the outdoors."
Most illegal guides were coming from overseas and working under the radar by telling Immigration New Zealand they were only here as tourists, he said.
"A lot of people hide behind the fact of saying we're not actually taking people fishing, we're just going for a walk along the river with them and it's very hard to prove - but we know they are getting reward for what they are doing."
Anglers were flocking to New Zealand in numbers never seen before, Mr Smith said.
Rising numbers brought an increased risk of something going wrong and meant there was a real urgency to tighten rules, he said.
The agency responsible for deciding whether a guiding license was needed was Fish and Game.
Chief executive Martin Taylor said following representations from professional guides, the Fish and Game Council would now consider bringing in a license.
"I'm guided by my council, so when my council comes out with a conclusion then I'll do what my council want me to do. So I'm completely neutral on it."
A decision on whether to bring in a licence would be made within the next six months, he said.