United Airlines has announced that it is temporarily suspending PetSafe, its program for pets that travel in cargo. The news comes shortly after a United flight attendant reportedly told a passenger to place their dog in the overhead bin, resulting in the animal’s death.

The airline says it is conducting a “thorough and systematic review” for pets that travel in cargo and is partnering with independent experts in pet safety and travel. While the review is being conducted, United will not accept any new reservations for pets traveling in cargo, but existing reservations will be honored. The statement says United will “assist any customer that wishes to cancel their reservation,” though it’s unclear if that means the company will issue refunds. United expects the review to be concluded by May 1st.

This suspension does not affect pets that travel within the main cabin, though United says this service will also be under review. The company has already announced that beginning in April, it will issue brightly colored bag tags to better identify animals that are traveling in-cabin.

United has misplaced two dogs traveling by cargo in the past week alone

United transports the most animals out of any major carrier, and has the highest rate of animal deaths. Even when accounting for the larger volume of animals transported, the airline has still had the highest animal death rate of any US airline for the past three years, at 1.19 deaths per 10,000 animals transported. That’s higher than the second and third US airlines that transport the most animals per year — Delta and American — combined. In addition to animal deaths, United has also misplaced two dogs traveling by cargo in the past week alone. One was supposed to head to Akron, but was instead put on a St. Louis flight, while the other was headed for Wichita, but ended up in Japan.

United also recently tightened its rules around bringing support animals on planes. The airline now requires passengers to provide evidence that the animal has been vaccinated and “been trained to behave properly in a public setting and acknowledge responsibility for the animal’s behavior.” These rules are in addition to providing 48 hours’ notice to the airline along with an enhanced letter for the passenger from a medical professional.