The Chinese airline Kunming has been scrutinized after photos were released of female flight attendants lying in overhead compartments as part of a "hazing ritual," The Washington Post reports.

The photos were released by a popular app called Wechat and went viral in China over the weekend. The ritual reportedly started five years ago and “marks the employees’ first 30 to 50 hours of flight service,” according to The Post.

Only the women undergo the hazing by male colleagues "who force the female attendants into their compartments, sometimes even closing the lid on them," the Wechat post reports.

Kunming Airlines released a statement Monday apologizing for the incident and said they had no knowledge of the ritual and it was solely the act of the flight staff “conducted after flight hours,” The Post reports.

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But the Wechat post claims that the airline knew about the ritual and flight attendants have made previous complaints to flight management.

Many Chinese airlines have strict standards for female flight attendants, which include that women must be between 5 feet 2 inches and 5 feet 7 inches tall and must weigh between 110 and 115 pounds, The Post reports.

Kunming Airlines added in their statement that they plan to discipline the flight staff involved in the incident.

Read more at washingtonpost.com