Opponents of B.C.'s plan to combine the federal and provincial sales taxes into the Harmonized Sales Tax officially launch their drive to defeat the levy.

The clock is now running on the initiative petition spearheaded by former B.C. premier Bill Vander Zalm.

He has 90 days to collect signatures from 10 per cent of registered voters in every riding in the province.

If successful, the Liberal government could be required to hold a referendum on its plan to link the seven per cent B.C. tax and five per cent federal tax into a single 12 per cent assessment.

Vander Zalm says 5,000 volunteers are ready to help collect the required signatures, but University of B.C. political scientist Richard Johnston notes there has never been a successful drive under B.C.'s 16-year-old initiative legislation.

Critics of the Harmonized Sales Tax say it will increase the cost of many items currently exempt from provincial taxes.