Investigators say the employee of the Lake Tobias Wildlife Park in Halifax, Jackson Township, stuck her arm into a fenced-in area and the tiger responded by either biting or scratching her arm.
She has suffered a deep wound.
The zoo owner says the employee - who is in her 20s - is a driver, and is not allowed to do what she did.
The two tigers at the zoo have been there since they were cubs.
Lake Tobias offers safari-like tours of wildlife and exotic animals in a rural setting.