Chairman Lester Levy says some Aucklanders have enjoyed "historically incredibly low fares" unavailable to others, so 3 per cent of the region's public transport passengers face consequent rises.
Commerce Commission officer Hayden Nash told Mr Shields that although his complaint "may raise issues under the Fair Trading Act", it did not intend taking action "at this time".
But he said the matter may be suitable for consideration by the Ombudsman, who had jurisdiction over council organisations such as Auckland Transport.
"When we decide whether to open an investigation, we consider how widespread, blatant and damaging the issue appears to be, based on the information available," he wrote.
"While we won't be taking any action at this time, we will record the information you provided us and may use it if we get similar complaints in the future."
Mr Shields questions that logic, saying the Fair Trading Act should be upheld regardless of how widespread any breaches may be.
Although Urban Express and Birkenhead Transport are the only bus companies so far covered by Hop, Auckland Transport says the system will ultimately extend to other fleets, and monthly passes can already also be used on trains.
But the organisation has yet to put a date on the full Hop rollout, after running into technical difficulties, and Mr Shields believes he should not be charged extra for a service yet to be delivered in full.
Auckland Transport announced an indefinite delay just days before a planned rollout to Ritchies Transport and North Star buses last month, blaming an "intermittent technical issue".
A spokeswoman said last week that French technology provider Thales had identified the problem and was "working on the fix".
But she could not say how long it would take.
New monthly fares
$140 single zone
$190 two-zone
$250 three-zone