Federal New Democrats are calling on B.C. voters to urge their MPs to stop the harmonized sales tax before it comes into effect July 1.

New Democrat MPs Libby Davies and Don Davies handed out postcards in Vancouver on Saturday that people could send to their federal representatives in a bid to block the HST.

Libby Davies told reporters the federal Conservatives and Liberals rammed through the harmonized sales tax bill last December with little debate.

Organizers of an anti-HST petition in B.C. have collected 600,000 signatures and signed up a minimum of 10 per cent of registered voters in all 85 provincial ridings.

Davies said the grassroots initiative, led by former premier Bill Vander Zalm, has likely stunned MPs who supported the controversial tax.

She said now it's time they listened to voters.

The HST is also set to be introduced in Ontario on July 1.