A September 2014 decision by the High Court relating to Harding ruled that an investigation and disciplinary hearing could continue even when a member resigned.
Last year, a long-awaited police probe concluded no criminal charges would be laid despite "significant" design deficiencies.
In 2015, the Attorney-General filed for a judicial review of the Ipenz' decision.
"It is important that we clarify the law as to whether a professional can avoid disciplinary proceedings by simply resigning," then Building and Housing Minister Dr Nick Smith said in March 2015.
"Completing the Ipenz investigation will also be important in clarifying the professional standards expected of a senior engineer supervising the work of a more junior engineer."
The Attorney-General is seeking to have the Ipenz decision overturned and for Engineering New Zealand to complete the investigation into the professional conduct of Reay's role in the design of the CTV Building.
Engineering New Zealand says it will abide by whatever decision the court makes.
Professor Maan Alkaisi, whose wife Maysoon Abbas died in the collapse, is expected to give a media statement on Monday morning before the hearing begins on behalf of the CTV Families Group.
Alkaisi is still battling for "justice and accountability" seven years after the tragedy.
After the police decision not to pursue a prosecution, he vowed: "We will never give up until justice is done."