The action was being taken because the National Party had described Ambrose's actions as unlawful or unethical.
He's needed to take this action because the National Party in particular has been describing his conduct as unlawful and unethical," Mr Mansfield said.
"This is obviously damaging his reputation and ability to work."
Mr Mansfield said the legal action was to protect Ambrose.
"Work is all that he has. So rather than be political fodder and not being able to respond, he's done what's responsible and gone to the court to seek a ruling."
Mr Key has laid a police complaint over the recording, saying it was illegally made, and police said today they would execute search warrants at four media outlets for any material they might have related to it.
Despite mounting pressure to release the contents of the tape, Mr Key and Mr Banks have refused to discuss what was on it.
NZ First leader Winston Peters today revealed what he said was on the tape.
Mr Mansfield said Ambrose was yet to be contacted by police.
If a judgement is made saying the meeting was not private, police will be unable to prosecute.
Key stays silent
Earlier today on the campaign trail in Whangarei Prime Minister John Key continued to refuse to answer questions about the details of his conversation with John Banks.
He said repeatedly that it was a matter for police and, in reference to the future of Don Brash, that that was a matter for the Act Party.
He continued to claim that the only interest in the teapot tape came from the media.
He stood by his comments comparing the recording to News of the World tactics and his comments earlier in the week about how, if he consented to the publishing of the tape, it could in some circumstances lead to suicide.
But Mr Key did not repeat his suicide comments today saying only that "it would lead to bad outcomes".
In response to a claim that suicide support groups have found his comments offensive and asked for an apology Mr Key said "I feel very strongly about the principle involved."
"[The media] have to have ethics in the way [they] operate in this country and I believe that wasn't on display last Friday."
Mr Key said he was happy to work with either Don Brash or John Banks and the leadership of Act was a matter for the Act caucus.
He acknowledged that the possibility of an overseas post was raised with Brash when National first took office but he had not had "a conversation on that in recent times to the best of my knowledge."
National avoids questions on the tape
Mr Key underlined his determination not to buckle to pressure and release tape by yesterday twice walking out on journalists in the face of questions.
And it's been followed this morning by pulling his party president out of a radio interview.
In what may be a major test of his political judgment, Mr Key appeared prepared to dig in his heels and stand firm on his position - a tactic that could inflame the issue with only nine days until the election and New Zealand First on the rise in the polls.
National Party strategists this morning cancelled an interview Radio New Zealand's Morning Report programme had secured with the party's president, Peter Goodfellow.
In an email, Jo de Joux said 'National was interested in talking about the issues that mattered to New Zealanders - a tape we believe was illegally recorded is not one of those'.
John Key's political opponents called yesterday's walkout of a press conference unprecedented and damaging to Mr Key's credibility, and increasing speculation that the pair's conversation included derogatory comments about Act leader Don Brash and the elderly who support NZ First.
Mr Key yesterday became defensive and called the issue a "sideshow". He claimed that media interest in the story did not square with the public's interest in other election issues including the economy.
After a walkabout in Upper Hutt with National's Rimutaka candidate Jonathan Fletcher, Mr Key answered a handful of questions on the teapot tape before ignoring further ones and jumping into his limo.
Earlier in the day, he dramatically walked out of a press conference after side-stepping questions about the tape, saying each time that he wanted to focus on issues such as the economy.
The teapot story and video of the press conference were the most popular items on the Herald website yesterday, and the story is a hot topic on social networking sites.
NZ First leader Winston Peters continued to hint at derogatory comments he claims to know were caught on the tape.
"Dumping on your publicly announced coalition partner's leadership is serious," Mr Peters said. "Dumping on old people who have done so much for this country in their younger days, in trying times, is serious."
In a speech in Whangarei yesterday, Mr Peters mocked the PM's claim that he could not recall discussing NZ First supporters or elderly people with Mr Banks.
Labour leader Phil Goff said Mr Key's tactic was a window into his credibility, and the public had a right to know if the pair had discussed the future of Dr Brash's leadership.
"Be honest with the electorate beforehand what they're trying to do, not afterwards. For a Prime Minister to storm out of a press conference is unprecedented, I think, in my time in politics.
"I can't remember a Prime Minister going back to Muldoon that was so brittle they couldn't take the heat of answering valid questions from the news media. That's his job."
Mr Key said consenting to the release of the tape would jeopardise his ability to "get out there and meet people all of the time. I would have to be on the lookout for [covert recording devices] every second."
He has suggested that giving his consent to publish the tape could lead to tragedy.
"What happens if a couple of high profile New Zealanders have a conversation about their son or their daughter being suicidal - a Sunday paper reports that and that child takes their own life?"
But the Media Freedom Committee - which represents mainstream media organisations - condemned the comparison yesterday.
"To suggest this case could lead to much wider publication of private conversations, even raising the subject of suicide, was unfortunate and totally wrong," secretary Tim Pankhurst said.
He said the matter could be resolved if Mr Key or Mr Banks consented to publishing the contents of the tape "to let voters be the judge of its importance".
