Are late fees for paying rent late illegal?

Late fees are not illegal.  Usually, late fees are assessed to tenants that fail to pay rent on time.  the duty to pay the late fee is contractual in nature.  in other words, the tenant is not obligated to pay a late fee unless the parties agree in the lease.  if there is a lease and there is a late fee penalty then the landlord is able to enforce this penalty.  if there is no lease, the landlord is not permitted to assess a later fee unless there is a state statute.  i am not awar of any such state statutes that permit a later fee on a month to month tenancy.  If there is a lease that has this late fee clause the landlord may evict you for failure to pay the fee as it is a breach of the lease.  i suggest that you hire a lawyer to review the lease and determine whether there is a valid penalty late fee.