Sparrow is spokesman for a group of about 150 accountants who have called themselves Accountants Deferring the Decision (ADDs). The group has set up a website called 'Say No To One Institute'.
The ballots are open until October 30 but, even if members held off their vote until the last day, that was still not enough time to fully read through and then adequately debate the Explanatory Memorandum, Sparrow said.
ADDs feels NZICA should have released the information weeks ago to allow for proper consultation with members.
Between May and July, NZICA and ICAA carried out eight weeks of consultation by holding face-to-face roadshows, webinars, accepting submissions and by polling members.
The Australian body has 73,000 members and of NZICA's 33,000 members, 448 were polled on the phone and 1711 polled online. This was a random sample taken by an independent polling company.
The polling found 88 per cent of ICAA and NZICA members said the proposal should be put to a vote. Of those, 66 per cent of NZICA members indicated they would vote for, 14 per cent against and 19 per cent were undecided.
But Sparrow said not enough information had been made available during that consultation period.
"How could we argue against it when they were saying they had a compelling case? I mean, if it was so compelling why have they taken until the end of September to come out with the information?"
"This is a board proposal, it hasn't come from the members," he said.
Craig Norgate, chief executive of NZICA, said on Tuesday that members had been given enough time to read the paperwork before having to vote.
"There are an awful lot of them that want to get on and start voting now. The rest have five weeks. It's a lot easier to read than you'd expect," he said.
Norgate said the merger would result in lower fees and a more powerful organisation for Kiwi members.
Sparrow said he was concerned with NZICA's ambition to be "a world player".
"There's no question of whether the All Blacks have to join up with the Wallabies. New Zealand bats above its status all the time, apart from losing the America's Cup."
He said New Zealand and Australia were totally different countries in terms of taxation and politics and merging the two made no sense.
"We just need to talk and discussion gets results and something could be modified. This is too important to at least not get some debate happening."
If members vote in support of the merger, implementation of the so-called One New Institute is expected to begin next year.