Progressive Conservative Leader Brian Pallister says the party has retained the services of lawyer Robert Tapper.
Pallister suggests that the NDP government has skipped a step in the legal requirements needed to raise the PST to eight per cent from seven.
The tax increase was to come into effect Monday, but the bill that would make it law has not passed in the legislature.
Current legislation requires a referendum before the tax can be increased, but Bill 20 would retroactively eliminate the need for such a vote.
Tapper says legal action can't go ahead unless the bill passes in the legislature and becomes law.