The Secret Files of the Spy Dogs S01 E11 "Small" or "The Secret File of the Diminutive Doggies"

The fleas offer to make peace with dogs. So Ralph, Mitzy and Von Rabie are shrunk down to meet with the fleas. But they're shrunk down too little and the fleas kidnap them to hold for ransom. The Bark Squad is then shrunk too to save our heroes.