Progressive Conservative Leader Brian Pallister suggests the NDP government has a false mandate since it promised in the 2011 election campaign that it would not raise the PST.
The government announced in April that it would raise the sales tax to eight per cent from seven per cent.
It also said it would change a law to eliminate the need for a referendum first.
The next election is not scheduled before the fall of 2015, but Pallister says the government should call one now to let Manitobans vote on the sales tax.
The government has said the increase is needed for infrastructure projects and to maintain front-line services.