It depends on the case. If the unit isn't rent-controlled or stabilized, then landlords can increase the rent as much as they want as long as they send a notice if the increase is by 5% or more.
The notice will vary depending on the leases:
Yearly Leases - 30 days of notice
Leases Between One and Two Years Old - 60 days of notice
Leases Longer Than Two Years - 90 days of notice
However, if the tenant lives in a rent-controlled or stabilized unit, the landlord will have a cap on how much they can increase rent, and that cap depends on what the government sets each year.