I have a paying California tenant with a now unauthorized dog

[Jeffery Pete]

I have a paying California tenant with a now unauthorized dog. Claims they only take care for friends? I have pictures

I have noticed these dogs in the past. The tenants may indeed be house sitting these dogs for extra money. However they are in the apartment and sometimes in the common areas while being supervised by the tenants.

This is in violation the rental agreement. I would like to keep paying tenants but I have no Pet agreement and pet security deposit.

What steps should I take with them to rectify the situation?

Is there a notice of violation I should serve at this point?

Any help you can provide would be greatly appreciated!