If you believe that your employer has committed a criminal act, then you can report that act to law enforcement and you are protected from termination of employment.
Merely complaining to the employer is generally insufficient -- though in your case, if by city animal shelter, you mean "animal control," i.e., the law enforcement agency charged with the protection of the public safety with regard to animal regulation in your municipality, then a complaint to the shelter would in fact be a complaint to law enforcement.
You may want to consider bringing a formal complaint, so that there is a public record.
Note: Of course, we all know that despite there being laws protecting employees from sanction for reporting the bad acts of their employer, employers have ways to harass "difficult employees." So, don't think that just because the law may protect you, that you may not have to fight to protect yourself -- because you almost certainly will.
I'm not suggesting for an instant that you not complain -- just that I don't want you coming back here with your hair on fire, if things don't go smoothly.
Hope this helps.
NOTICE: My goal here is to educate others about the law. I am always available to answer your follow-up questions after you click Accept – however, if you do not click Accept, the website gets paid, and I receive nothing. This is true, even if you are on a subscription plan. So please click Accept, so that I will be able to continue to provide this service for others in the future.
And, if you need to contact me again, please put my user id on the title line of your question (“To Socrateaser”), and the system will send me an alert. Thanks!