Lease rules
Can my landlord ban pets?
Yes, no-pet policies are legal almost everywhere - but they cannot be applied to service animals or emotional support animals, which aren't pets under fair-housing law.
Landlords can prohibit pets, restrict breeds or sizes, and charge pet fees or pet rent where state law allows. What they can't do is refuse a documented assistance animal, or charge pet fees for one - federal fair-housing rules treat that as disability discrimination.
Hiding a pet is a genuine lease violation that can support eviction, so negotiate instead: offers of a pet deposit, renters insurance with pet liability, or references from a prior landlord change many nos to yeses.
Do something about it
The Lease dictionary: pet deposits turns this answer into action.
General educational information, not legal advice. Laws vary by state and city and change over time - for a specific situation, contact a local tenant-rights organization.