"Mr Key and National know they face humiliation in the referendum. This latest flag flying ploy shows they are desperate not to be losers.
"To fly the referendum flag winner beside the New Zealand flag is an exercise in deception and suggesting that it has the same status. Legally it has none."
Transport Minister Simon Bridges said he approved the request from the Flag Consideration Project to fly the alternative flag on the Auckland Harbour Bridge alongside the current flag from January 22 to March 24.
"The proposed alternative flag will be flown alongside the current flag each day on the Auckland Harbour Bridge until the end of the referendum period, except for Waitangi Day when the current flag will be flown alongside the Tino Rangatiratanga flag."
Presently, only three flags, alongside the New Zealand flag, are allowed to fly on the Auckland Harbour Bridge -- the Tino Rangatiratanga flag on Waitangi Day, the Australian flag on Anzac Day, and the Merchant Navy flag on Merchant Navy Day.
Earlier this month, a Weekend Herald editorial called for the alternative flag to be flown from the Auckland Harbour Bridge, arguing that the "most visible poles in the country" should be utilised to give people an idea of how the flag looks in real life.
The silver fern flag with black, white and blue colours will go head-to-head with the existing flag in a second referendum in March, which will decide whether New Zealand changes its flag for the first time in more than 100 years.
Whether New Zealanders choose to ditch or keep the current flag, March 24 will bring to a close a process that officially began in October last year when Prime Minister John Key announced that a two-stage referendum would be held on the issue.