Some HOA (or condo associations) have decided (by a vote of the homeowners) to establish a rental cap or ceiling. Different communities have different caps or ceilings (one might be 25% while another is 35%, etc). Some communities have not established rental cap or ceiling, it really depends upon where the townhouse is located. Many times thoses ceilings/caps are there to protect the investment of the owners so that there are not too many renters.
If the townhome is actually a part of a condominium association then many times the ceiling/cap is in place so that the owner will be able to sell in the future. FHA & VA have guidelines that if more than a certain percentange of a condo association is rentals than they will not allow loan money.
If you have any more questions, feel free to contact me at 757.532.3351. Good Luck