Wait and see

With the political scene in British Columbia seeming to have been significantly reshaped by the HST petition campaign, it was only a matter of time before the issue was raised again on the federal level despite the Harper Cons' attempts to distance themselves from the tax. And the NDP has found a key area where the Cons can obviously make important decisions one way or the other despite their protestations to the contrary:

Federal NDP Leader Jack Layton sent a letter in April to Prime Minister Stephen Harper, urging him to put off implementation of the tax until the referendum process is complete.
...
(NDP MP) Don Davies said there's no rush to bring in the tax before a possible referendum takes place, especially in light of the petition, which he called “one of the greatest expressions of public democracy in British Columbia history.”

“The least that Mr. Campbell and Mr. Harper can do is respect that by not proceeding with the HST on July 1,” he said.

“We think that the only democratic thing to do and the only smart public policy thing to do is to stop this tax now and let's wait and see what the people of British Columbia decide to do.”

Of course, the agreements signed to implement the HST seem to have been nicely structured to allow each side to claim that it's locked in by the other. But there can't be any room for doubt that the governments involved can override their agreement to impose the tax without considering the views of the public if they're both willing to do so. And it makes all the sense in the world to keep the status quo in place while the petition/referendum process plays out, rather than converting the province's tax system so as to make it costly and complicated to de-harmonize sales taxes again.

That is, unless the Harper Cons plan to hold B.C. to the terms of the agreement even in the face of a massive popular revolt against the HST. But if that's their choice, then it's only fair that they'll have to face the political consequences. And the NDP is nicely positioned to speak along with the public in condemning any decision to force the HST ahead.