The country’s largest estate agents’ association, NVM, has broken ranks with the rest of the sector over how homes should be sold, reigniting a dispute about transparency in the bidding process.

Last week, the NVM published a protocol for bidding on houses that departs from agreements previously made with other industry bodies and the housing ministry, which it aims to introduce from February next year.

The protocol retains a bidding method under which only the selling agent can see and register bids while a house is on the market. NVM estate agents are responsible for some 70% of Dutch house sales.

That approach has drawn sharp criticism from homeowners’ lobby group Vereniging Eigen Huis and rival agents’ body Vastgoed Nederland, which say it is open to manipulation.

They argue that agents can use insight into bids to play buyers off against one another or tip off others shortly before the deadline, the Financieele Dagblad reported on Monday.

The VEH and Vastgoed Nederland favour an approach in which all bids are kept secret until after the deadline, as agreed in talks with the government and real estate sector groups last year.

The VEH says the NVM’s protocol is a step backwards, offers too little transparency and “offers no protection to consumers looking to buy a home”. Vastgoed Nederland says the NVM’s move will fragment the market and leave buyers uncertain about the bidding process.

The NVM, however, says keeping bids secret harms sellers and offers buyers false reassurances. It wants its new protocol to become the industry standard.

The VEH has now called on politicians to intervene, and parliament has already backed a motion to standardise the bidding process in law.

Caretaker housing minister Mona Keijzer has urged the sector to resolve the issue itself, but says it will be up to the next cabinet to decide whether stricter regulation is needed.