OTTAWA — Assuming it's a full house, the vote to scrap or save the controversial long-gun registry is going to be a nail-biter.

Last November, Conservative MP Candice Hoeppner's private member's bill to scrap the registry passed second reading with the support of eight Liberals and 12 NDP MPs.

The Liberals are being whipped, and two New Democrats have decided to change their vote, putting the bill's passage in doubt.

Here's how the vote could break down:

Of the 308 seats in the House of Commons, three will be vacant for the vote — formerly one Liberal and one NDP who supported the registry and one Conservative.

Of the 305 remaining seats, 75 Liberals, 48 Bloc, 26 NDP MPs — 149 total — will likely vote to save the registry.

A total of 153 votes are needed to win the vote for either side.

On the Conservative's side, all 143 Conservatives will vote to scrap the registry, and independents Helena Guergis and Andre Arthur are expected to do the same.

The Liberals say three NDP MPs are now expected to vote to scrap the registry again, meaning there are 148 votes to kill it.

Hoeppner believes there are as many as seven New Democrats on board, which would give her bill 152.

That leaves either three or seven NDP MPs potentially up for grabs who have all voted to scrap the registry before.

If it comes to a tie, Liberal MP and Speaker of the House Peter Miliken will be asked to cast his vote.

"I'll know when I walk into the House of Commons and I see who's sitting in their seats, that's when I'll know how it will go," Hoeppner said. "If we even have one or two Liberals not show up, that would be it."

Liberal MP Frank Valeriote, who launched a new online campaign to try to coerce the NDP to save the registry, agreed it's going to be close.

"I think it's going to be a nail-biter, frankly, right up to the moments before the vote," he said.

bryn.weese@sunmedia.ca