ACT MP Simon Court committed a "clear breach" of select committee confidentiality, Parliament's powerful Privileges Committee has found.
However, Court apologised to the committee in a letter and it has not recommended further action against him.
The Privileges Committee is a group of high-profile MPs from all parties which considers and reports on questions of privilege relating to Parliament and MPs, such as breaches of Parliament rules. Privileges are powers and immunities which ensure Parliament is independent of the Crown and the courts.
Court was referred to the committee in June after he revealed in a media release the result of a vote by the Environment Committee.
The vote related to Court's suggestion to include a definition of "matauranga Māori" in the Natural and Built Environment Bill, one of the replacements for the Resource Management Act.
The committee found it was a "clear breach" of confidentiality.
"We find the member's actions in this matter to be concerning, and cavalier," the committee's report said.
Court had argued the information could be shared because it no longer related to business still before the Environment Committee, which had been unable to resolve the matter itself.
In his letter to the committee on 27 June, Court accepted the Speaker's interpretation and apologised for the disclosure, admitting he had relied on an incorrect reliance on Standing Order 243(3)(a).
The rule says closed select committee proceedings may be disclosed if they do not relate to business or decisions that are still before the committee.
Court also suggested the breach could have been avoided if the rule included an additional requirement for MPs to seek clarification about disclosures, but the committee rejected this.
"The member should not have relied on any interpretation of Standing Order 243(3) because the vote was self-evidently a proceeding on a bill that had not yet been reported to the House," the report said.
"The Standing Orders are sufficiently clear and do not require any amendment to require or remind members to consult with the committee or committee staff.
"Members are expected to inform themselves of all of their responsibilities under the Standing Orders and to seek advice on the application of parliamentary rules where necessary. We note that the member did not do so in this case, and has admitted that it would have been appropriate..."
The Privileges Committee said they did not think the matter warranted further debate in Parliament, but said it had served as a "timely opportunity to reinforce for members the expectations that apply to confidential proceedings and the reasons why they exist".
The committee referred to the rules laid out in the 2003 report by the Standing Orders Committee, which said draft reports and closed sessions of select committees must remain strictly confidential.
This was in part because premature or selective release of committee proceedings could increase the risk of lobbying outside normal processes, or give advantage to particular groups or persons.
Court was the second MP to be referred to the committee in a month after an investigation into Education Minister Jan Tinetti's delay in correcting statements to the House.
Tinetti was forced to apologise after she was found to have misled Parliament due to a "high degree of negligence".
However, she was not guilty of contempt because, the committee found, the error was most likely unintentional.
RNZ
