Elections BC says the labour dispute at Canada Post has yet to impact the province's mail-in harmonized sales tax referendum, but that could change if the lockout doesn't end soon.

Don Main said Wednesday if the dispute is not resolved by the end of next week, Elections BC will consider extending the voting period for the referendum.

Ballots for the referendum are supposed to be received by more than three million eligible B.C. voters by June 24, with the deadline to return the ballots to Elections BC by July 22.

Elections BC officials have said earlier they have the legal authority to change the referendum dates if required.

Main said Elections BC is also aware that federal Labour Minister Lisa Riatt said the Conservative government was poised to introduce back-to-work legislation as early as Wednesday evening, meaning the dispute could be over by early next week.

Canada Post locked out members of the Canadian Union of Postal Workers on Tuesday night, suspending mail service right across the country after nearly two weeks of rotating strikes by the union.

Main said Elections BC and Canada Post officials discussed the labour dispute and the HST referendum during a conference call. He said Canada Post assured Elections BC the referendum ballots currently in the mail system are secure.

"If the strike were to go on four to five days, then we'd need to re-examine changing the dates of the referendum itself," he said. "Right now, if the strike only carries on that amount of time, we'll still be able to meet our deadline to get the ballot packages out to voters by (June) 24."

The first HST ballots were mailed on Monday and voters who received them can return the completed package to any of the 60 Service BC centres around the province.

The combined tax was introduced by the Liberal government in July 2009, on the heels of a provincial election that made no mention of the tax, and has been law in British Columbia since July 1, 2010.

A successful petition campaign led by former B.C. premier Bill Vander Zalm forced the referendum under the province's direct democracy laws. The laws, unique to B.C. in Canada, allow voters to mount petition drives that can force byelections to recall politicians or hold provincial referendums or political votes to overturn some laws.

More than 500,000 British Columbians signed the petition last spring calling for the repeal of the HST.

The referendum question asks: "Are you in favour of extinguishing the HST (Harmonized Sales Tax) and reinstating the PST (Provincial Sales Tax) in conjunction with the GST (Goods and Services Tax)?"

Both pro- and anti-HST camps are now busy trying to woo voters with town halls, advertising campaigns and campaign-style political gatherings.