To set the cat among the pigeons? No problem. But does this variation have the same meaning, that is, to cause alarm, discomfort, or consternation? I reread the story:
Having done so, I had to presume it has the same meaning as the cat-pigeon one. The cat (the watchdog, haha!) has created unease among the chickens (the slaughterhouse operators) by embarking on an investigation into possible price-fixing among them.
But guess what? Cats, according to this story below, get along with chickens!...
Why it’s okay to put a cat in the henhouse
And, putting a twist on the cat-pigeon idiom but sticking with the cat-chicken idiom, this People's Daily story has this admonition:
'Don't put cat with the chickens'
It's fascinating what one can uncover online.
I'll wrap up with this:
The Cat's Pajamas? 7 Purrfect Idioms