"As a consequence, the form of the hearing may be truncated, and the nature of the disciplinary committee's findings more limited than if Mr Harding had remained a member," an IPENZ statement released today said.
Mr Smith's office said he was "disappointed and concerned" at the last-minute move.
"He is of the view that it is unacceptable for professional people like Mr Harding to simply resign and walk away when they are being held to account," a spokeswoman for his office said today.
"This would not be possible for any building designed after 2002 but the old Engineers Registration Act effectively enabled a person to avoid accountability in this way.
"The situation reflects the inadequacies in the Act and reinforces the Minister's determination to make changes to the system by which engineers are regulated."
Mr Smith will make announcements regarding reforms before parliament rises at the end of the month.
Mr Harding was employed as a building designer by city firm Alan Reay Consultants.
His boss, Alan Reay, also resigned from IPENZ earlier this year, resulting in an investigation into his role in the CTV collapse being dropped.
A separate hearing conducted by Chartered Professional Engineers into Mr Harding's re-assessment for continued registration as a chartered professional engineer in 2011 is intended to proceed as planned.
Mr Harding's lawyer Michael Kirkland did not return calls from APNZ today.
Today IPENZ said that since it can no longer make disciplinary orders it was free to make public comments about the CTV building.
It said the Canterbury Earthquakes Royal Commission conducted a thorough investigation related to the CTV building and fully accepts the findings.
It specifically accepted that the regulatory system of the day placed no restriction on who could undertake design work, with the relevant requirement being to meet the by-laws of the Christchurch City Council which were a set of technical standards and requirements.
Membership of IPENZ was entirely coincidental and formed no part of the regulatory system.
But it stressed that the powers made available by the passing of the Chartered Professional Engineers of New Zealand Act 2002 mean its rules are much stronger.
"As the registration authority, IPENZ has disciplinary jurisdiction over both current and former chartered professional engineers for their actions taken whilst on the register," it said.
