The GCSB bill has passed the committee stage in Parliament this evening and will go for its third and final reading tomorrow afternoon.
The Bill, which will introduce new powers to the Government spy agency, is expected to pass by one vote thanks to the support of United Future leader Peter Dunne.
Labour leader David Shearer had been pushing for last-minute changes to the bill, calling for citizens' right to be spelled out in the new law.
But Prime Minister John Key responded that he did not think it was necessary.
Labour's proposed changes came after Mr Key gave an assurance that access to New Zealanders email content would be restricted when the GCSB was carrying out its cyber security role.
The Prime Minister has promised to resign if there are any major mistakes.
"But the facts of life are& that won't happen."
Mr Shearer reached out to Mr Dunne this morning in a last ditch effort to change bill.
But it wasn't soon enough, Mr Dunne said.
"I only received notice of it this morning, that is far too late for a serious amendment of this type."
MPs urged to break rank
Speakers at last night's meeting in the Auckland Town Hall, which attracted more than 1000 people, urged MPs to vote against the proposal.
"I think it will pass unless there is a brave National MP who's not following John Key blindly into disaster," internet entrepreneur Kim Dotcom told the meeting.
"Maybe we'll get lucky and one of those 50 National Party members will have a conscience," added Green Party co-leader Russel Norman.
However, ONE News Deputy Political Editor Jessica Mutch said it was unlikely the meeting would change the way MPs vote.
"It would be a pretty brave National MP that would cross the floor over this issue, but whether they genuinely think they can change MPs minds, that's probably a little naive," she told TV ONE's Breakfast.
Mutch said the Government has to rush the process through as there is currently no legislation for the GCSB.
"We're in limbo, and in an ideal world it would be great if we could get cross-party consensus," she said.
"Politically the Government has to rush this through and they're in this precarious position where they have to get this through with just one vote."
Once passed, the GCSB Bill and its related legislation will extend the agency's powers so it can provide support for the New Zealand Police, Defence Force and the Security Intelligence Service.
But meeting organisers and the Opposition contend that the bill will allow for "mass surveillance" of people's emails.
However, Mr Key has given assurances that will not happen.
"Will there be wholesale surveillance of people's emails, where they receive those emails from and the content of those emails? I can categorically rule that out," he told a press conference yesterday.
The GCSB bill passed its second reading by 61 votes to 59 on August 1, after ACT leader John Banks and independent MP Peter Dunne agreed to support the Government.
The Government won Mr Dunne's support after agreeing to make several major amendments to the bill.
The revised GSCB bill now includes a code of principles for the spy agency to follow as well as the introduction of an oversight panel.