The Commerce Commission is looking into whether Wellington International Airport Ltd breached the Commerce Act by awarding the city's largest taxi company a priority lane at the airport.
The commission has received several complaints about the Airport's decision to give Combined Taxis the best operating spot.
Wellington Combined Taxis says it went through a fair tender process, but some companies say they were not offered the chance to submit a tender.
Last month the airport company said the new layout was designed to make it less congested and safer for customers, not to push out smaller cab companies.
But companies such as Kiwi Cabs say their business has halved because they have to operate in less desirable lanes.
Kiwi Cabs says small companies never stood a chance of winning the priority lane.
The commission says it has yet to decide whether a full investigation into the tender process is warranted and at this stage is still making routine enquiries.