The Selinger government had run the numbers on raising the provincial sales tax five years before they actually did it.
The revelation came during an exchange between Opposition Leader Brian Pallister and Premier Greg Selinger in a budget estimates meeting Friday morning.
Pallister said information acquired by the Tories shows government officials looked at the economic viability of raising the PST in 2008-09, in 2009-10 and in 2010-11 before the Oct. 4, 2011 general election.
The documents, obtained through the Freedom of Information and Privacy Act, were not released to the Tories because they contain internal analysis for cabinet eyes only.
Pallister said the information the Tories do have shows the government had long been interested in increasing the PST and was planning to do it once the 2011 election was over.
"The fact that they have documents proves beyond a shadow of a doubt that they discussed the issue," Pallister said. "At the very least we now know that the NDP cabinet, at the most senior level of government, discussed raising the PST prior to the election, denied they would and then proceeded to raise it."
During the 2011 campaign, Selinger said it was "total nonsense" the NDP would raise the PST.
Selinger said Friday the decision to raise the PST one point to eight per cent last year was made after the 2011 election when it became known it would cost up to $1 billion to improve flood protection following the 2011 spring flood in western Manitoba and the Interlake.
"We did not have any specific recommendations or plans to raise the PST before the last election," Selinger said.
He also said finance officials, acting on their own, routinely look at various options for improving the province's bottom line, but without making recommendations to cabinet regarding how to implement them.
The Tories are fighting the PST hike in court because they claim it was made without holding a referendum as outlined in the 1995 Taxpayer Protection Act. The first court date on the Tories' lawsuit is April 25.
Pallister would not comment on what evidence the Tories have that would convince a judge the NDP acted illegally.
A similar challenge last year by supporters of the Canadian Wheat Board, to reverse Ottawa's end of the agency's monopoly, was rejected by the courts. At issue was whether federal Agriculture Minister Gerry Ritz broke the law by ending the CWB monopoly without a vote by farmers.