Postal workers rejected Canada Post's latest offer Monday, as their union scrambled to avert a looming strike. (Andrew Vaughan/Canadian Press)

Elections B.C. says a looming strike at Canada Post could delay or extend a mail-in referendum on the province's harmonized sales tax.

Canada Post has received 72-hour strike notice from the union representing postal workers, meaning the workers are in a legal strike position on Thursday.

Three million HST referendum ballots are to be mailed out in mid-June, with the ballots to be returned by July 22. However, the dates could be extended if there's a postal strike.

B.C.'s acting Chief Electoral Officer Craig James says he has powers to extend the dates to return the ballots if a strike does happen.

The referendum will ask British Columbians if they want to repeal the HST and go back to the previous combination of the provincial sales tax and the GST.

Critics say the tax is unfair because it cuts the taxes paid by business while increasing the tax burden on consumers.

In order to increase support for the HST the government recently promised to cut the rate from 12 to 10 per cent, hike corporate taxes and send out one-time rebate cheques of $175 to families for each child and to low-income seniors.