The council is to look into Iris Robinson's behaviour as a councillor
Castlereagh Council will meet later to decide on the terms of its inquiry into the conduct of Iris Robinson.
Last week, the BBC reported that, while a councillor, MP and MLA, Mrs Robinson procured money from two developers to help her teenage lover open a cafe.
She then sat in on a meeting of the council when it decided to award a lease for the Lock Keeper's Inn in south Belfast to Kirk McCambley.
She broke the law by not declaring her financial interest in the venture.
ROBINSON STORY SO FAR
6 January: Peter Robinson says his wife Iris tried to take her own life last March after admitting an affair with teenager Kirk McCambley
7 January: BBC's Spotlight reveals details of Iris Robinson's financial affairs - she obtained £50,000 from two property developers to help her lover launch a café and asked him for £5,000 for herself
10 January: DUP says Iris Robinson is receiving acute psychiatric treatment
11 January: Peter Robinson steps aside from his role as first minister for a six-week period - DUP colleague Arlene Foster becomes acting first minister amid renewed focus on resolving her party's problems with Stormont power-sharing colleagues Sinn Fein
The Alliance party group on the council have already written to Northern Ireland's main public spending watchdog, the Comptroller and Auditor General, to ask for a full and independent inquiry.
Meanwhile, it has emerged that one of the property developers from whom Mrs Robinson obtained money for Mr McCambley once donated money to the DUP.
Ken Campbell said he contributed between £4,000 and £5,000 to the party several years ago.
He said he had never donated any money to Iris or Peter Robinson personally.
Mrs Robinson obtained £50,000 from Mr Campbell and another developer Fred Fraser, who died last year, to finance Kirk McCambley's cafe in south Belfast.
She kept £5,000 for her herself and then, when their relationship ended, she demanded Mr McCambley pay the money back.
On Monday, lawyers for Mr Campbell said the money had been loaned to Mr McCambley on an interest-free basis and that £20,000 had been repaid. The remaining £5,000 is still outstanding.