In certain situations, a landlord may not be able to enforce a no-pets clause.

Most standard leases and rental agreements contain no-pets clauses. Such provisions are legal everywhere, and courts generally allow a landlord to evict a tenant who acquires a pet in violation of a lease clause and refuses to give it up.

In certain situations, however, a landlord may not be able to enforce a no-pets clause if the dog is already living in a rental unit and/or:

• The landlord tries to add a no-pets clause to a rental agreement
• The landlord tries to enforce an existing no-pets clause, after knowing about but not objecting to a tenant's dog for a significant period
• The landlord agreed, no matter what the lease says, that the tenant could have a dog
• The tenant can prove that keeping a dog is necessary for security or health reasons.

You don't want to go to court to argue about any of these theories if you can possibly avoid it. So if a landlord tries to get rid of you or your pet, sit down together and try to work things out. You may end up paying a little more rent or putting down a bigger security deposit, but it will be cheaper than court. If you need some help negotiating, try a community mediation center or the local humane society, which may provide mediators specifically for landlord-tenant disputes about pets.

Adding a no-pets clause to a lease

Even though landlords may refuse to rent to someone with a pet, it's harder for a landlord to change the rules if a tenant already has a pet. The landlord's legal right to change the terms of the tenancy usually depends on whether you signed a rental agreement or a lease.

A lease lasts for a specified time. Neither the landlord nor tenant can unilaterally change its terms while it is in effect. When the lease comes up for renewal, generally a landlord is free to change its terms. (But, as discussed below, a landlord who hasn't objected to a dog for a long time may have lost the chance.)

A rental agreement is open-ended. Commonly, it runs from month to month, and allows the landlord to change the terms of the rental agreement with 30 days' notice to the tenant. Local rent control ordinances, or the rental agreement itself, may limit the landlord's right to make such changes.

Some special local rules may apply, however. Some cities recognize that adding a no-pets provision is often just a way to get rid of a tenant for another reason, have restricted the practice. Check your local ordinances or call the city to find out.