Hi there! I volunteer at the local Human Society. Are you familiar with them?
Yes, it's my understand that they are a nonprofit based out of Washington D.C. that address animal-related cruelties and resolve animal welfare issues by applying resources.
I enjoy taking care of the cats and dogs at my local shelter. I wonder if they help any other types of animals?
Yes, as of 2001, they deal with the fur trade and wildlife abuse as well as cats and dogs.
I understand some people don't like them very much, though. Are there any controversial aspects of their work?
I'm not sure. You may be thinking of PETA (People for the Ethical Treatment of Animals). They can get pretty aggressive. 
Ah, perhaps that's it. Does HSUS protest experimentation on animals?
Yes, they aim to stop animal or human suffering due to cruelty and testing. 
Are they are large organization? 
They were identified as the 136th largest charity in the US by "The Chronicle of Philanthropy" in 2013.