When announcing his review, Key said he believed it was essential for him as Minister of Tourism and Prime Minister "to protect New Zealand's international reputation".
In response, up to 500 adventure tourism operators were told to pass the stringent new safety audit by November, after which it would be an offence to operate without one.
Outdoors New Zealand, the sole provider of the safety audits, has told operators it cannot accept new applications. It is struggling to deal with the "hundreds" of applications outstanding.
Deputy chairwoman Josie Ogden Schroeder told the Herald on Sunday that up to 60 per cent of operators could fail to pass the requirements in time unless there was more money from the Government.
Auditors need training and more administrative staff brought in to deal with the backlog, she said.
"We have people working between 60 and 70 hours a week on the audits but we just cannot handle any more at this time and have had to put a pause on things," she said.
"Last year we were left as the only audit provider after other companies pulled out. Many of our staff need training for the new systems and that would cost about $500,000. At present, we are running at a loss."
About 130 operators had been certified since the audits were introduced in 2011, Ogden Schroeder said.
The owner of a Queenstown adventure tourism business, who declined to be identified, said he had spent several weeks putting together an application for a safety audit but had no idea if it would be approved.
"Getting operators through this audit is a big job. It could be devastating for tourism in general if this doesn't all happen when it is supposed to."
WorkSafe New Zealand oversees the project for the Government and more audit providers were being sought.
WorkSafe spokesman John Tulloch said: "We are in discussion with other prospective companies and will continue to work with Outdoors NZ."
The Prime Minister's office acknowledged on Friday "some difficulties". A spokesman for Key however insisted any companies failing to meet the November target through no fault of their own would not be punished, but declined to say if the deadline would be extended.