Federal NDP leader Jack Layton speaks at the British Columbia NDP Convention in Vancouver on Sunday. (Darryl Dyck/Canadian Press)

The NDP really doesn't want anyone to forget it is firmly and clearly against the harmonized sales tax.

So, in an rare move, Jack Layton will hold a joint press conference with British Columbia NDP leader Carole James and Ontario NDP leader Andrea Horwath to denounce the tax that is set to be put into place in those two provinces come July of next year.

There are strong anti-HST movements in both those provinces -- and the NDP is supporting them.

The HST legislation was tabled by the government in Parliament today, meaning it will be voted on some time next week.

But the NDP is trying to make the most on this issue politically, given the potential trouble that looms for the federal Liberals.

Michael Ignatieff has made it clear to his caucus that the party will be voting for the tax and that it is a whipped vote, meaning everyone has to play ball.

Problem is at least one Liberal MP, Keith Martin, also from B.C., is considering opposing the legislation already. He didn't show up for yesterday's ways-and-means motion on the HST, which was really the first step towards next's weeks vote.

And another B.C. Liberal, Hedy Fry, says she hasn't made up her on mind on how she'll vote, either.

So, the NDP is jumping in with both feet, launching ads over the weekend and holding this multi-leader press conference Monday to remind Canadians they don't support it.

Chances are, they'll be reminding Canadians as much as possible over the next few weeks.

UPDATE: