A landlord is furious at the Ministry of Foreign Affairs and Trade for protecting a foreign diplomat who owes $20,000 in rent and damaged property.

The Tenancy Tribunal ruled in favour of Wellington landlords Matthew Ryan and Rebecca Van Den Bos' after they sought reparations from a former tenant.

But the Ministry of Foreign Affairs and Trade (MFAT) has now intervened, saying the proceeding should never have taken place because the tenant has diplomatic immunity.

OPINION: The Soap Box: Why did MFAT even get involved in rental case?

MFAT's lawyers have sought a rehearing, and their appeal will be heard by the tribunal next month.

Ryan said MFAT's intervention was deeply unfair, and he was now unsure whether he would get repaid for his losses on the Karaka Bays rental.

"I'm really disappointed," he told Newstalk ZB. "If [MFAT] felt that they had a legitimate case then they should have turned up to the first tribunal hearing.

"I just don't feel like it's cricket. For them to step in and for her to hide behind some sort of immunity."

Ryan said he had expected a high-ranking diplomat to be a reliable tenant.

"I thought I had the security of a three-year tenure but they left [after eight months] with rent arrears, they caused some damage to the property before they left, gave me no notice of leaving.

"And so effectively I was left high and dry. I thought the Tenancy Act would at least allow me to recover the rental shortfall and the damage.

"And so it's pretty disappointing to hear that when you lease to a diplomat you effectively have none of the provisions that you would normally have it [it were] a normal member of the community."

A tribunal ruling released last month said the diplomat had rented the "high quality" property, which is valued at $1.5 million, for $1500 a week. She had a fixed-term lease until September but left the property early.

The landlords successfully applied to get back the unpaid rent until the house was tenanted again – a total of $17,357. They also successfully applied for the costs of damage to blinds and an internal lift, and the cost of an alarm callout when the tenant was overseas.

The tenant did not turn up to the hearing.

MFAT's lawyers appealed the decision and asked for a rehearing, the tribunal's report said.

"MFAT seeks the order to be set aside on the basis that the proceeding should have not commenced, and no decision issued against the tenant, on the basis that she is a diplomat, and immune from any action in a civil proceeding in New Zealand."

Ryan said MFAT's response set a poor precedent.

"It's concerning for any landlord who looks at renting a property to a diplomat," he said.

"They could effectively do anything they want to your house, they could use it as a P house, they could carry on with illegal activities and you'd have no redress because they'd hide behind some sort of diplomatic immunity."