Housing inspectors conducting a sweep of flats in Dublin have found the vast majority of flats inspected to be in breach of regulations.
They have visited 589 flats on the North Circular Road and issued warning letters in respect of 483.
Dublin City Council says its "intensified inspection programme" will involve up to 6,000 rental units over the next three years.
The inspections involve a number of different housing regulations but laws that came into effect at the start of the month have also made it illegal for landlords to rent out bedsit accommodation.
All rental properties now have to have their own bathrooms.
Failure to comply with the laws can mean maximum penalties of a €5,000 fine or a six-month jail term.
Of the 483 warning notices issued so far, 220 have been followed up with improvement notices.
If improvement notices are not complied with, the council can issue a prohibition notice ordering the landlord not to re-let the flat until improvements are carried out.