Projet Montréal Leader Valérie Plante says "not a penny" of public money will be spent on a new baseball stadium — unless Montrealers agree to it.

Plante said if elected, her party would hold a referendum on the issue during the next election, four years from now.

"We love baseball. We want a team in Montreal, but we're not going to use Montrealers' money without consulting them," she said, standing in front of a novelty cheque for $500 million made out to MLB and "signed" by Denis Coderre.

Plante accused Coderre, who has been vocal about his plans to bring a Major League Baseball team back to Montreal, of negotiating with the league behind taxpayers' backs.

The total cost to build a new stadium could easily be in the range of $500 million, if not more. It's unclear what percentage of that cost would come from the public purse.

Plante said that's her main issue: many parts of the plan appear to be unclear.

While it looks as if things have been moving forward, evidenced by recently released mock-ups of a new stadium, Coderre is keeping residents in the dark, she said.

No business plan has been made public. Projet Montréal asked the mayor as recently as Monday how much public money would go into paying for a stadium, but it hasn't received a response.

Spectre of Formula E?

The lack of transparency, Plante said, is reminiscent of how the city handled the Formula E race.

That event, held in July, has been shrouded in secrecy. The city and promoters have been tight-lipped about details regarding ticket sales and the final cost, saying those details won't be ready for months.

"We've seen it with the Formula E that when my opponent becomes an event promoter, he's really bad at it, so we don't want that happening again," Plante said.

Projet Montréal introduced the idea of holding a referendum on the stadium issue earlier this year.

Rumours have been swirling about just how close the Expos are to returning for years, but only a few people know for sure. (Ryan Remiorz/Canadian Press)

Details about the plans to bring a team back to Montreal have been kept hush-hush, with many observers saying the league prefers to keep its negotiations under wraps.

Commissioner Rob Manfred has said on a number of occasions that Montreal would be a great candidate for an eventual expansion team, but the city would need a new stadium.

Plante said she's all for the idea of baseball returning to the city, but she's also into the transparent administration of public funds.

"We have limited financial resources, and there are many needs. Public transport … is a priority, housing is another one, so yes, a baseball team, but not at any cost."