Trent Wotherspoon says the bill calls for an independent watchdog for P3s and would require the full cost of a project be publicly reported.
Wotherspoon says that would allow governments and the public to go into the deals "with eyes wide open."
"The concern right now is government's pushing forward with these P3 schools. In fact, they have part of the process already out there, (requests for qualifications) that are out, and they don't have the facts on the table to Saskatchewan people," Wotherspoon said Monday.
"And so we believe a spotlight needs to be put on those facts."
The proposed legislation would also prevent P3s from moving ahead if there were less than three bidders.
"One doesn't allow competition," said Wotherspoon.
Infrastructure Minister Don McMorris, who is also minister responsible for SaskBuilds, said P3s can work without legislation.
McMorris hadn't seen the bill tabled by the NDP, but said Winnipeg Mayor Sam Katz and the Manitoba Heavy Construction Association found similar legislation in Manitoba problematic.
"They just said it was so restrictive that they didn't feel that any P3 could meet the criteria that was set out and move forward," said McMorris.
"We see examples in other jurisdictions that don't have tough legislation like this, strict legislation like this, that have been very transparent.
"Our process will be very transparent. I mean evaluation done at the start through an independent firm, a national accounting firm, a fairness adviser. And once the (request for proposals) are all said and done, so that there's no competitive issues, we'll release all that information."
Premier Brad Wall announced last month that nine joint-use schools would be built through public-private partnerships.
A joint-use school is one where public and Catholic schools could share things such as gymnasiums, practical and applied arts spaces, band rooms or daycares, while having their own teaching space and staff. The idea is to share maintenance costs and save money; however, the exact model for the nine new schools is yet to be determined.
Construction could take about four years, but Wall has said the P3 model means schools can be built faster and for less money.