Hundreds of property managers across the country are signed up to a private social media page where landlords blacklist tenants despite the claims of bad behaviour being unverified and some posts potentially breaching privacy rights.

Property managers from throughout the country and at every level within the industry are looking at the social media posts.

Renters United spokesperson Robert Whitaker says this is deeply worrying.

"Property managers are shortlisting by any mechanism they can. If they have to choose between 20 people, if the name's familiar because they have been seen in this group, they are going to be struck off."

He says while a property manager may not be consciously using the list, it can create unconscious bias.

Too often, people are discriminated against because of their ethnicity, name, a disability or their appearance, he says.

The Property Management Institute of New Zealand declined an interview but in a statement says it does not endorse members joining these pages.

It has reminded members they should be following established vetting processes rather than engaging in online and unverified gossip, it says.

RNZ contacted some of the big firms, whose members are subscribed to the page.

Harcourts turned down an interview.

In a statement, Ray White says it does not support the use of unregulated platforms or pages and that should evidence be provided that a franchisee has breached the privacy rights of any tenant it would investigate this.

It says Facebook groups have no affect on its existing tenant application, vetting and selection process.

Barfoot & Thompson agreed to an interview.

Its general manager of property management, Samantha Arnold, says she was not aware their members were signed up to this Facebook page, but that she does not believe it has been used for vetting tenants.

"If it is for vetting, it is not ethical and it's definitely not something we would want to be using for verification, at all."

Staff have been asked to quit the page immediately, she says.

"A bad tenant could be just someone's opinion, and it could be just a clash with the owner. That's exactly why we wouldn't rely on someone else's information, because it's opinion at the end of the day, rather than fact. We would much rather see a tribunal report to see if there have been any rent arrears."

But Rob Whitaker says merely telling property managers to stop using the pages does not address the real issue.

"What this shows is there is no ethical base to these companies. Their individual agents should already have enough professional ethics to know joining these groups is totally inappropriate. Saying 'we're telling our members to leave that group' doesn't address the broader problem of ethics in this industry."

He says he wants to see managers reporting inappropriate posts online.

The property management industry is barely regulated.

But prior to last year's election, the Labour Party promised to introduce a code of conduct for the industry.

In a statement, the Ministry for Housing and Urban Development says work is underway on this and the minister will be given advice in the coming months.

In the meantime, the Privacy Commission will be cracking down on information sharing in the rental market.

Privacy Commissioner John Edwards says landlords and property managers hold more power in the current rental market, and they must act carefully.

"It can effectively lock people out of the rental market on the basis of information they don't know even know a prospective landlord has access to. That would be unfair.

"We do see cases where people can be tainted by an association with a co-tenant or abusive partner and that can marginalise people who are vulnerable and disempowered."

Edwards says tenants are entitled to know what information a group or landlord has about them.

If the landlord or group does not hand it over, or destroys it, that could be a criminal offence.

Edwards says the Privacy Commission's focus will be ensuring a high standard of compliance within the sector.

-RNZ/Eva Corlett.