Croydon landlords have launched a legal challenge against selective licensing in the borough.
A group of landlords operating as the Croydon Property Forum applied early in June for a judicial review of the decision and will argue the consultation process was flawed.
Licences costing up to £750 for five years are due to be introduced in October.
The council claims the licences, which will require every private landlord in the borough to prove they are "fit and proper" for the role, will cut down on crime and anti-social behaviour caused by poor property management.
Gavin Dick, local authority policy officer at the National Landlords Association, which has been advising the Croydon landlords, said: "I don't think Croydon has an endemic anti-social behaviour problem across the entire borough and I don't think the council has demonstrated that being linked to the private rented sector.
"They have not answered that fundamental question."
A judge is expected to give rule whether there is an initial case for a judicial review by mid-July.
A council spokesman told the Croydon Guardian: "We are confident that our landlord licensing scheme is robust, lawful and will raise housing standards across the borough, and we’ll continue preparing to launch this scheme from October 1."
Want to comment on this story? If so...if any post is considered to victimise, harass, degrade or intimidate an individual or group of individuals on any basis, then the post may be deleted and the individual immediately banned from posting in future.