Labour's Corrections spokesman Kelvin Davis has identified himself as the MP who Corrections felt potentially put a female prison officer in danger.
However, he denies that copying an ex-prisoner into his email correspondence with the Corrections officer put her in danger - saying her name was already known to the ex-prisoner, and her generic work email address would have been easy to work out as a result.
Corrections Minister Judith Collins yesterday wrote to all MPs, after Corrections approached her to express concern about the incident.
Ms Collins also asked MPs who wanted to visit prisons to go through her office to make arrangements - something the Green Party and Labour have objected to.
In the letter, Ms Collins wrote that she recently became aware of an email sent by an MP to a female Corrections staff member.
"This email openly copied in an offender with a long track record of criminal behaviour, including violence against women. This potentially compromised the safety of the staff member."
Ms Collins told the Herald that Corrections raised the matter with her. She would not name the MP in question, but Mr Davis was happy to put his hand up.
He said he had been approached by an ex-prisoner, who said he had been the victim of violence in Mt Eden prison in 2013 and was attempting to secure CCTV footage of the incident from Corrections.
He did not know the ex-prisoner's criminal history at the time.
Mr Davis said he had seen letters about the matter between the ex-prisoner and the Corrections officer, who he later emailed, copying in the ex-prisoner.
Because her name was already known to the offender, and Corrections used generic work email addresses, Mr Davis did not feel he had revealed any new information, or put the officer in any danger.
In the letter circulated today, Ms Collins also covered how MPs should organise visits to prisons.
"Requests for visits should be directed via the Corrections Private Secretary in my office. They will ensure the right people in Corrections are contacted and will facilitate the arrangements for your visit," she wrote.
"The Prison Director is the most appropriate person to guide you during your visit. Our prisons contain the country's most difficult and dangerous people.
"Take some time to familiarise yourself with prohibited items. For example, cell phones, tobacco, lighters and recording devices are prohibited in a prison."
Green Party corrections spokesman David Clendon has taken umbrage at that instruction, saying by law all MPs are entitled to visit prisons - and if he wants to do so urgently he will ignore the instructions.
"I am concerned by this letter, I think it is quite a heavy handed approach. It indicates to me that the Minister is trying to exert control over MPs' access to prisons.
"The legislation is quite unambiguous. As MPs, as of right, we can enter a prison any time to inspect the condition of a prison or check on the wellbeing of inmates."
Mr Clendon said he was happy to follow the procedure outlined in the letter for routine prison visits, but in future cases where he wanted to visit a prison urgently he would not.
Labour's deputy leader Annette King was also unhappy with Ms Collins' instructions, saying she felt it was an attempt to exert control over opposition MPs.
Ms Collins said she first sent a letter to MPs with the same advice in 2009, after an issue with another MP. The advice aimed to make prison visits easier and also give the opportunity to visit more areas of a prison, she said.
"[Mr Clendon] can do what he likes. As long as he sticks to the law, that's fine. This is saying, if you want to look around the prison and those sorts of things, you have to be aware that the Prison Director is in charge of safety."