Delta Air Lines is instituting a stricter policy when it comes to emotional support animals.
Passengers must now provide a veterinary health form or vaccination record along with a letter signed by a doctor or licensed mental health professional stating the passenger's need for the animal. A statement regarding changes to the policy was released in January but set to take effect Friday.
The number of support animals on planes has jumped in recent years, and so has the number of incidents with those animals.
In January's statement, Delta said it has experienced an 84 percent increase in reported animal incidents since 2016, including incidents of biting.
"The rise in serious incidents involving animals in flight leads us to believe that the lack of regulation in both health and training screening for these animals is creating unsafe conditions across U.S. air travel," said John Laughter, senior vice president for corporate safety, security and compliance for Delta Air Lines.
United Airlines began enforcing similar restrictions in February.