JNTO has released information for travellers following the introduction of the Private Lodging Business Act (colloquially known as the 'Minpaku Law') on June, 15 2018.
The Private Lodging Business Act (hereinafter “PLB Act”) came into effect in Japan on June 15, 2018.Following the introduction of the law, activities for reservations at accommodation facilities not covered under either the Inns and Hotels Act or the new PLB Act are now unlawful. As a result, reservations for such rooms made through online booking websites may be subject to cancellation.
It is possible to confirm whether the accommodation facility you have booked through an online booking website is correctly licensed or registered by enquiring directly with the website.
In Japan a variety of accommodation options are available and it is easy to secure alternative accommodation, including private residence rentals correctly registered under the PLB Act, in case it becomes necessary for you to change your booking.
See here for a list of accommodation search websites, which list only correctly licensed registered accommodation facilities in Japan.