United Airlines said it is reviewing an incident aboard one of its flight during which a woman claims she was told to incorrectly sit her child facing forward in a car seat.

On Sunday, Cassie Hutchins-Brosas shared on Facebook she was preparing to board a flight from Denver International Airport with her 8-month-old daughter when a gate agent took issue with the use of a car seat.

She said because her daughter is only 18 pounds, she flies her in a rear-facing car seat. However, an agent told her neither she nor her daughter could stay on the flight unless they turned the car seat forward.

“They told us that the plane could not leave without us moving it, so I knew we would be kicked off if we did not comply,” she wrote in a post published on Facebook.

In a statement sent to USA TODAY, United said they were reviewing the incident. “Our customers’ safety is our top priority, so we have already been in touch with the customer and the relevant flight staff to learn more about what happened.”

In an update to her Facebook post, Hutchins-Brosas said United would refund her daughter’s plane ticket.

According to United’s website, passengers can use car seats on planes so long as it conforms to “all applicable Federal Motor Vehicle standards.”

A Federal Aviation Administration page on Flying With Children said any child restraint systems used on flights must be installed on a forward-facing airline seat, and placed “in the appropriate forward- or aft-facing direction as indicated on the label for the size of the child.”

Discussions over bringing car seats on flight have increased after an adult female passenger was killed last month when she was almost sucked out of a Southwest Airlines flight that experienced an engine explosion. The incident ignited debate over whether children under 2 years old are safe to stay seated on a parent’s lap during flight or should use safety restraints such as a car seat.