The answer to this question depends entirely on how long you have been a tenant there. The magic number if you are a landlord is one year. If you are a tenant, it's anything less than a year.
During the First Year of the Tenancy
In general, the landlord may NOT require a new or increased security deposit. However, there are two exceptions: (1) The landlord MAY require an additional deposit IF the landlord AND tenant agree to modify the terms and conditions of the rental agreement to permit a pet or for other cause AND the additional deposit relates to the modification. (2) The landlord MAY landlord collect a security deposit that was listed in the rental agreement but has not been paid yet.
After the First Year of the Tenancy
The landlord MAY require a new or increased deposit BUT the landlord must give the tenant at least three months to pay.