A public meeting about a recent decision to drop trains as an option for quick and congestion-free transport to the airport is expected to attract hundreds.
But Auckland Transport says it won't be attending because it would interfere with its "neutral position" on the option.
Campaign for Better Transport is holding the meeting on Tuesday evening to discuss the opposition to the decision.
In June, the boards of Auckland Transport and the New Zealand Transport Agency voted to eliminate the $2.6 billion commuter rail network option in favour of a $1.3b light rail or a bus option.
But the spokesman for the advocacy group, Cameron Pitches, said they believed the report the boards based their decision on was flawed.
"It's clear that catchment and capacity figures for heavy rail have been understated in the report.
"For instance, the report states that the capacity of light rail and heavy rail could be the same by 2046, but the report overlooks the ability of our electric trains to run as six-car sets, effectively doubling potential capacity."
Pitches said up to 200 were expected to attend the meeting and they were advising people to get there early to ensure they got a seat.
Speakers at the public meeting will include:
• Graeme Easte, Campaign for Better Transport
• Mike Lee, Auckland City Councillor and AT Director
• Graham Matthews, General Manager Airport Development & Delivery at Auckland Airport
• Jim Jackson, The Onehunga Enhancement Society
• Stu Johnson from the RMTU
Auckland Transport was invited to attend but a spokesman told the Herald the meeting was within the electioneering period and it "endeavours to hold a neutral position for all meetings".
"As there is one election candidate speaking we consider this to conflict with our neutral position.
"Auckland Transport has made its position clear on the preferred way forward for airport transit and that report is attached," the spokesman said.
The meeting will be held on Tuesday August 30, 7.30pm at the Pearce Street Hall, 3 Pearce St, Onehunga.