Canada's marriage application form uses the terms "applicant" and "joint applicant".
California proposed the terms "Party A" and "Party B" when its state Supreme Court legalised same-sex marriage in 2008, but the court's decision was overturned by a referendum a few months later.
Mr Mead said the department would also have to change its computer systems to record the sex of the parties to a marriage, change its brochures and websites about marriage, and train registry office staff.
Gay people from as far afield as Auckland and Christchurch plan to be at Parliament for the historic moment, expected to be between 7.30pm and 8pm on Wednesday, when the same-sex marriage bill passes its final reading.
"We are expecting people perhaps to be spilling out to the venues around Parliament," said Marriage Equality Campaign spokesman Conrad Reyners.
The bill's opponents are making a concentrated last-ditch effort to stop the change.
Family First director Bob McCoskrie said more than 15,000 people had signed a web-based pledge to vote against any electorate MP who supports the bill, and against any party whose leader supports it.
All party leaders except NZ First leader Winston Peters supported the bill at its second reading last month.
New Zealand would become the 13th country to legalise gay marriage if the legislation passes.
Uruguay became the 12th this week.
Several states in the United States, Brazil and Mexico have legalised same-sex marriages, but no Australian state has done so, and a bill in the federal Parliament in Canberra was defeated 98-42 last September.
The New Zealand bill, sponsored by Labour MP Louisa Wall, passed its second reading on March 13 by 77-44 and Mr McCoskrie conceded that he faced "an uphill battle" to get 17 MPs to change their minds and stop it.
A Herald-DigiPoll survey published on March 26 found a dramatic shift in public opinion on the bill.
Support dropped from 59 per cent in January to 49.6 per cent, and opposition rose from 38 to 48 per cent.
"We always hold out hope," Mr McCoskrie said. "I think we have turned the public debate, but the political debate is far harder because they just don't want to listen."
Internal Affairs asked the select committee to delay implementing the bill by six months so it could make changes to forms and procedures, but the committee decided it should come into force four months after it is signed by the Governor-General.
If the bill is signed next week, it would take effect in August. Mr Mead said Internal Affairs was confident new forms would be ready by then.
Counting down anxious partners await decision
Andy Jalfon and Skot Barnett will be on edge on Wednesday waiting to see if they will be allowed to marry.
"People will be nail-biting after what happened in Australia," said Mr Barnett, 37.
He and Mr Jalfon, 32, plan to invite friends to their central Auckland apartment on Wednesday night to watch Parliament debate the final reading of Louisa Wall's bill to legalise same-sex marriage.
But they are not taking anything for granted, after a similar bill was defeated in Australia last September.
"Even though we are only five days away now, what if something terrible happens?" Mr Barnett said yesterday.
"In Australia, the first two rounds made it look as if it would continue, then it just completely fizzled out."
Mr Barnett, an employment transition consultant, and Mr Jalfon, a film-maker, met last year through the Gay Auckland Business Association, and say they are not interested in a civil union.
"We have never looked at a civil union because it's not the same," Mr Barnett said.
"To be honest, we haven't really got to the point of going 'let's get married', but what is really important for both of us is having the right to make that decision when it comes up."
The men refer to each other as "partners" and hope they can use that term if they marry, rather than "bride" and "groom" - "Who would be the bride?" Mr Jalfon asked.
Both their families wrote letters to MPs supporting Louisa Wall's bill, even though Mr Barnett's family is Catholic.
"My family has always been completely supportive, which is a big milestone because I come from a relatively religious family," he said.
Mr Jalfon said his parents were shocked when he told them, in his final year of university, that he was gay. But they got used to the idea.
"My folks love Skot and he's part of the family."
An Australian-born member of the Campaign for Marriage Equality, Jackie Russell-Green, said many gay Australians would come to New Zealand to marry if the bill passed.
