Composite: Depositphotos.com, A.Babii, REFIRE
Berlin's CDU/SPD coalition has announced what would be Germany's first comprehensive rent register, covering approximately 1.7 million rental apartments. The ambition is clear: use artificial intelligence to systematically identify illegal rents and enforce tenant protection at scale. The problem is equally clear: the proposal may be unconstitutional — and if a legal challenge succeeds, it could end up raising rents rather than lowering them.
That paradox has defined the debate since the announcement in late April by CDU parliamentary group leader Dirk Stettner and his SPD counterpart Raed Saleh.
Under the proposed law, landlords would register detailed information on a digital portal: address, floor area, furnishings, tenancy start date, net rent and service charges. AI would analyse the data automatically, flagging violations. Rents more than 20% above the local benchmark trigger notification to landlords and tenants; those more than 50% above it, a criminal offence under German law, are referred directly to the public prosecutor. Fines for non-compliance range up to €10,000 for individuals and €100,000 for large operators. Landlords would have twelve months to submit data once the law comes into force.
One significant gap has attracted criticism: furnished apartments and short-term lets are excluded from the current draft. Furnished listings fall outside standard rent controls, have more than tripled in supply since 2015 while unfurnished supply fell by over a fifth, and are precisely where the most aggressive pricing occurs. The Greens have called for their inclusion. Nothing comparable exists anywhere in Germany, though precedents exist in Scandinavia.
The constitutional catch-22
The legal challenge was set out in Die Zeit by Olaf Schmechel, a partner at GSK Stockmann in Berlin. "The current draft for the establishment of a rent register is unconstitutional," he said, identifying two distinct problems.
The first is self-incrimination. The register automatically refers excessive rents to the public prosecutor, creating an inescapable dilemma: refuse to submit data and face fines; submit it and potentially hand prosecutors the evidence for a criminal case. "The constitutionally protected right to remain silent would be rendered obsolete if the compelled submission of data could be used against landlords in criminal proceedings," said Schmechel. The Federal Constitutional Court has previously struck down similar measures.
Berlin's Senator for Urban Development, Christian Gaebler (SPD), dismissed the concerns as "nonsense", arguing that landlords are already required to provide information in cases of suspected profiteering and that the register represents "rights to information to which the State of Berlin is entitled." It is a tool for enforcement, he said, not a public database.
The second problem is more counterintuitive. A register covering all 1.7 million apartments would produce a far more comprehensive dataset than the existing Mietspiegel rent index. That larger database could be used to recalculate the local comparative rent — and it might turn out to be higher than the Mietspiegel currently indicates. "Then there would likely be a wave of rent increases," said Schmechel. "That would be the opposite of what the CDU and SPD actually aim to achieve."
A market problem in search of a political solution
The industry reaction has ranged from alarm to qualified nuance. The BFW Berlin-Brandenburg association described the register as "the birth of a Big Brother in housing policy"; Haus & Grund chairman Carsten Brückner called it "yet another ineffective bureaucratic monster" and accused the coalition of disguising its failures on housing.
The BBU Association of Berlin-Brandenburg Housing Companies was more measured. Board member Maren Kern said the goal was understandable but that "the legally sound and efficient implementation of this instrument is anything but trivial", warning the draft risks disappointing both tenants hoping for effective oversight and reputable landlords facing unnecessary bureaucracy.
The most surprising endorsement came from Vonovia, Germany's largest private residential landlord with around 140,000 Berlin apartments. "We welcome greater transparency, including through a register," said Sebastian Krüger, head of its eastern division. The support carries history: Vonovia has lost Berlin court cases over Mietspiegel violations, and its former CEO once called the index "faked." Charging an average of around €8 per square metre, the company has little to fear from scrutiny — and some interest in exposing competitors pricing less scrupulously.
For foreign investors, who make up a disproportionately high share of Berlin's residential landlord base relative to any other German city, the register introduces a specific compliance challenge. Submitting tenancy data in German, understanding the thresholds that trigger criminal referral, and navigating AI-driven enforcement all demand active legal oversight that many international owners have not historically required. Those relying on passive property management arrangements may need to revisit them.
Politics, timing and a poisoned chalice
The political context is difficult to ignore. The register was announced as part of 17 legislative projects agreed five months before Berlin's state elections in September 2026, when both governing parties are losing ground in the polls. "It comes just before the end of the Senate's term and, if passed, is to be implemented within twelve months," said Katrin Schmidberger of the Greens. The incoming government will inherit a law whose constitutionality remains actively contested.
Berlin is not acting in a vacuum. At the federal level, Justice Minister Stefanie Hubig's Mietrecht II package — targeting furnished apartments, index-linked contracts and short-term lets — has triggered its own wave of landlord opposition and a constitutional challenge, again from GSK Stockmann. The direction of travel at both levels is unmistakable: regulators are tightening their grip on a rental market they have long struggled to police.
What is not contested is the scale of the underlying problem. The Left Party's rent gouging app recorded more than 210,000 checks during last year's federal election campaign: over two-thirds of rents were at least 20% above the legal limit, and more than half exceeded the 50% threshold at which gouging becomes a criminal offence. Whether a rent register is the right instrument to address that, or a legal time bomb dressed as housing policy, may ultimately be for Germany's Constitutional Court to decide. Other German cities are watching carefully.