1. The effects may only be temporary.
This is more of a problem when the aversive stimulus used is mild.
2. It is not as clear of a source of information as is reinforcement.
Reinforcement provides the organism with more information than does punishment. Reinforcement tells the animal "what you did is good", while punishment tells the animal "stop that".
3. It may lead to escape, avoidance, aggression, & other negative emotional reactions.
The mechanism by which this occurs is called classical conditioning.
4. It must be prompt.
It should follow the occurrence of the undesired behavior immediately