When a guest refuses to register
You are the one the law holds responsible, so a guest refusing to provide their details is your problem rather than theirs. Most refusals come from believing the request is a scam, and are settled by explaining who is really asking. Where someone genuinely will not comply, you can decline to let them stay.
This is the most-discussed problem among owners, and the thing worth understanding first is where you stand.
The obligation is yours, not the guest's. If the details are not provided, it is you who has failed to report, and you who is exposed. The guest walks away from it entirely.
That is uncomfortable, but it also settles the question of how firm you are entitled to be.
Why guests refuse
Very few people are objecting on principle. In practice it is almost always one of four things.
They think it is a scam. A message from a stranger with a link, asking for a passport number and a date of birth, is exactly what a phishing attempt looks like. This is by far the most common reason, and it is a reasonable instinct rather than an awkward guest.
They believe hotels do not do this. They do, and always have. Anyone who has checked into a Spanish hotel handed over a passport at the desk and signed something. The only thing that has changed is that it now happens by form rather than at a counter.
They are worried about where the data goes. A fair question, and one with a good answer — see below.
They have simply not got round to it. Much the largest group, and not really a refusal at all.
What to say
Three things settle most of it, and the order matters.
Say who is asking. "This is a Spanish legal requirement — the Ministry of the Interior requires every accommodation provider to report guest details. It is not something we have chosen to ask for."
Say where it goes. "The details go to the Ministry of the Interior. Only the police, judges and public prosecutors can access them. We do not keep a copy of your passport." That is accurate — see the law in plain English.
Say that hotels do the same. "Every hotel in Spain does exactly this at the front desk. Holiday rentals now have the same duty."
What you are and are not entitled to ask for
You need the details. You do not need to keep their document.
You are responsible for the details being accurate and matching what they show you, so you do need to see the passport or have it shown to you. You do not need a photocopy, a scan, or a photograph — and Spain's data protection authority has said in terms that keeping copies is not permitted for this purpose. See what you must ask for, and what you needn't.
Saying that out loud often ends the conversation. A guest resisting "send me a photo of your passport" will frequently have no objection at all to giving you the number.
If they still will not
The reasoning owners rely on is straightforward: you cannot lawfully provide the accommodation without reporting who is in it, so a guest who makes that impossible has made the booking impossible.
Note what that puts on the guest: they are required to produce the document. And note what it puts on you: responsibility for the details being right, which you cannot discharge if nothing is produced.
The decree does not say in terms that you may refuse the stay, and we are not aware of a Spanish court ruling that settles it. What it does say is that you carry the duty and the liability. Cancelling is the position most owners take, and it is a defensible one — but if a booking is large or the guest is disputing it, take advice rather than relying on a web page.
Cancel rather than letting them arrive and hoping. A cancelled booking is an administrative problem. An unregistered guest already in your property is a breach you cannot correct afterwards.
The line that works
One owner in the Facebook group put it better than any script:
Nobody argues when an airline asks for a passport at the gate. Nobody suggests the airline is being nosy, or asks what they intend to do with it. It is simply understood that you cannot board without it.
This is the same thing. You cannot check in without it.
Cancelling a booking made through a platform
Cancelling has consequences on Airbnb and Booking.com that vary by platform, by your status on it, and by how late you are. Those rules are theirs, not Spain's, and they change — so check your own cancellation terms before you act rather than relying on what worked for somebody else.
What is worth knowing is that a guest refusing to meet a legal requirement is a stronger position to cancel from than most, and it is worth documenting the refusal in the platform's own messaging rather than by phone or WhatsApp. If you later need to explain the cancellation, you will want it in writing, where the platform can see it.