The union representing aviation security workers is worried about a lack of public knowledge about a new private company involved in airport security screening.
Secureflight searched Foreign Minister Murray McCully in Auckland when he was on his way to Washington in mid-March, despite him being a VIP travelling on a diplomatic passport.
The trip was one of the last official visits for the long-serving foreign minister, who officially steps down next week.
Mr McCully's office has blamed the Auckland Airport search on a local administrative error.
Secureflight director Peter Pilley declined to comment this week.
The E Tū union's aviation spokesperson, Kelvin Ellis, said he was not clear on what the firm's role was at Auckland Airport.
"It is concerning, from our perspective, to see a somewhat secretive and shadowy security organisation providing additional services.
"We'd really like some answers as to what screening they're doing, who's ordering it, who's paying for it and what... regulations Secureflight are actually operating under."
Mr Ellis said the powers of the company's workers were not clear.
"The Aviation Security Service employees carry warrants, they have special powers under the [Civil Aviation] Act to preserve aircraft safety and look after things.
"So it's really unclear what a private provider would be doing or what services they're providing that would be in excess or different to what AVSEC provide."
The Aviation Security Service (AVSEC) used to carry out the work now done by Secureflight, which was hired by airlines to carry out extra screening required by the US government.
AVSEC said the names of so-called 'selectee search' passengers were advised from the US to all airlines flying direct to US ports.
But it would not say whether Secureflight was operating under American or New Zealand law.
Air New Zealand was yet to respond to a request for comment.
Transport Minister Simon Bridges said yesterday he would not be investigating how his Cabinet colleague came to be searched before boarding the Air New Zealand flight.
Earlier this week, Prime Minister Bill English said he was sure there was no "negative intent" involved in the search of Mr McCully.
Mr English said he wanted to make sure the US understood there were protocols for people on diplomatic passports.
But he said random checks were part of border control and ministers should not be worried if they were searched.