[header] How to know if a rent increase is illegal [title] Get a copy of your written lease. [step] If you have a written lease, its terms cannot be changed while it is in effect. [substeps] Your lease dictates the amount of rent you may be charged during each month. 
It may also include notice provisions that require your landlord to send you written notice of an increase in advance. Typically your landlord will present a new lease within 30 days or so of the end of your lease.