Specifically, rent control laws that prevent you from raising the rent more then X% per year and laws that give someone automatic month to month terms after the lease expires..
This is because right now rental rates are artificially depressed. The landlord might have built their financial model on normal market rents. If someone can lock in a way under market rate due to the pandemic and then keep that rate after the pandemic, then the tenant is taking advantage of the market based pricing when it goes down but disavowing the validity of market based pricing when it goes up.
If rent control exemptions were create that allowed the landlord to raise the rent to what it was prior to the pandemic once this is over, then that would be fine. But as it stands, it doesn't seem fair to force the landlords to rent at under market rates (traditional market, i mean) and then also force that rate to be locked in for the future.