The second option is better: Black markets develop.
If the landlords has to rent their property below the expected return it will stop renting it and sale the property. Therefore, people wanting to rent property will have to agree on payments below the table. If impossible to sale or to increase rent they will stop maintenance and repair expense to increase profitability in expense of the quality of life of the peiople living there.
Resuming, they won't oblige to the norm either by withdraw from the market (stop renting) or reinvestment (maintenance)