The full meeting video is here. The Pluto debate and vote starts at 26:10 of the IAU meeting video.: https://www.iau.org/public/videos/detail/iau2006session2/
The IAU President and a small committee clandestinely and materially changed the naming resolution, kept it secret from dissenting members and the press, distributed the proposal just before the vote, rebuffed dissenters and concluded with a show of hands without an official count.
The entire International Astronomical Union session that resulted in the definition that demoted Pluto can be viewed on the video here. The voting discussion relative to Pluto begins at around 26:55 into the session. Most of the descriptive text below about the process was taken directly from the video of the debate and vote proceedings.
The vote was scheduled at the end of a 10 day conference in Prague when almost everyone had left. Only 424 of nearly 10,000 members remained.
IAU President, Ronald d. Ekers, opened the session stating that the IAU was asked to act on the planet definition issue. He stressed that prior proposals were delayed because cultural and popular issues needed to be considered.
Ekers stated that this was not just a scientific debate and that the issue cannot be resolved by science alone. "This is not just a scientific issue of what is correct. There is no correct answer to this question."
"The question is; what is a sensible compromise that will not just work for the professionals in the field but will work for everybody who is interested the sky, the planets, is curious, is educating and so on."
After Mr. Ekers and a panel member read two overwhelmingly positive and zero dissenting messages from colleagues on the pending resolutions he called for a show of hands however; 15 IAU members stepped forward to speak. The first 14 speakers were dissenting, and generally cut off by Mr. Ekers. The contentious and angry dissention included voters "not being properly consulted" and receiving the changed resolutions "just now as entering the session."
The response from Ekers; "the last step of the proposals was done in secret to keep them from the press." It seems that a lot of people were interested in this outcome and were getting in the way of the desired outcome of the rogue scientists.
These IAU members strongly dissented stating that the decision to vote was rushed, more debate needs to take place, the vote should be postponed and that "what was being presented was an insult to the entire astronomical institution."
The 15th and final speaker was recognized and stated that he was no scientist but that he wanted to say that the committee was doing a great job.
A movement by prominent scientists to meet mid-2007 to organize an electronic vote by the full membership did not succeed.