Dunedin Labour MP Rachel Brooking said the figures were so different to the original proposal for the medical school that "everyone is in the dark" and the business case needed to be released immediately.
The government would yesterday only say the business case would be released "soon".
In 2023, National pledged $280 million for a third medical school at Waikato University, with the university to raise a further $100m.
The government will now pour $83m into the new Hamilton-based school and Waikato University will have to find more than $150m for its contribution.
Ms Brooking said it was unclear how the government got to a point where the numbers had changed so dramatically.
"The government talks about a medical school with a focus on rural doctors, but at no stage have they referred to all the good work Otago University does in training rural doctors through their pathways programmes.
"Otago has been focused on a medical workforce that reflects our community."
Dunedin Mayor Jules Radich said he did not believe "we will ever see it".
The cost-effective decision would have been to put more money into Otago and Auckland’s medical schools, he said.
The Waikato medical school is expected to open in 2028, with its first intake tipped to be about 120 students.
"Now, it remains to be seen how well it works out, but it won't impact on the other medical schools — I don't think it will make much difference to Otago Medical School other than restricting the possibility of expansion that it certainly had."
Former Otago University academic Prof Robin Gauld, now executive dean of Bond Business School at Bond University in Queensland, said the public needed to have all the facts.
Most people would conclude this was a politically driven decision, he said.
"I think it's a blow to [Otago and Auckland universities] and their ambition to increase the level of training.
"They've said they could step up and do more if the support is there. But having said that the universities will continue to do what they've always done very well — which is to train world-class doctors."
Prof Gauld said in the short term, the decision to establish a new medical school could actually slow down the process of training new doctors, given that the investment would now be going into a new medical school rather than increasing placements in existing programmes.
A lot of the discussions would have happened behind closed doors, he said.
"I think Waikato was in a slightly less favourable or enviable position.
"They've obviously put together a kind of a business model that shows that they're going to reach some break-even or profit-turning position at some stage in the foreseeable future, maybe within the next five or 10 years."
