John Kerry, the U.S. special presidential envoy for climate, was caught not wearing a mask during a flight with American Airlines. Kerry was flying from Boston to Washington D.C. when he was seen reading his book in the plane's first-class section.

A photo of a maskless John Kerry was first posted by The Tennesee Star, and it sparked a debate from people on social media.

The American Airlines requires all its passengers to wear masks on board. This is in line with the Centers for Disease Control and Prevention and the Transportation Security Administration's directives, and President Joe Biden's executive order mandating face coverings during travel, New York Post reported.

Health experts also encourage everyone to wear face masks, and this practice must still be done even after getting a COVID-19 vaccine and maintaining physical distancing.

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John Kerry on United Airlines

A Twitter user has tagged the official account of American Airlines, asking to clarify the photo. American Airlines responded by saying, "Masks are required onboard our aircraft," adding that they are now investigating the matter by reaching out to Kerry.

The airline further noted that the crew did not observe Kerry not wearing a mask, and no customers alerted them about the non-compliance issue.

"Our mask requirement has been and will continue to be a critical component of our comprehensive effort to protect the health and wellbeing of our customers," said David Seymour, the Chief Operating Officer of American Airlines.

Seymour added that the mask requirement was not only to protect their customers but also their crew amid the coronavirus pandemic.

Travelers boarding a plane are allowed to remove their masks only when they are eating or drinking. However, the photo did not show that John Kerry was eating nor drinking. Instead, he was reading a book during his flight.

Many people were outraged at seeing Kerry without a mask even though he is not eating or drinking. Twitter user @stclairashely expressed disappointment, saying she hoped to have the "same privilege" as Kerry as she knew people who had been banned for life for not wearing a mask properly.

She added that a flight attendant harassed her during her last flight with the same airline because her mask was slightly off her nose. For his part, Donald Trump Jr. labeled the climate czar to be a "Liberal hypocrite."

John Kerry's Defense

The Washington Examiner reported that Kerry's actions would put him in violating the CDC's mandate for not wearing a mask during flights. Because of the controversy surrounding his photo, John Kerry explained what happened during his flight with the said airline. 

"Feels like there's some St. Patrick's day 'malarkey' afoot on Twitter. Let's be clear: If I dropped my mask to one ear on a flight, it was momentary," he tweeted on Wednesday night.

John Kerry added that he was wearing his mask because it saves lives and stops the spread of the virus, and it's what the science tells us to do."

However, his Twitter post was not able to convince most of the people on social media. A Twitter user, who was not happy with his response, urged him just to admit the mistakes he's done, and act as a special envoy. Meanwhile, the White House still has no comment regarding the issue.

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WATCH: Image Surfaces of John Kerry Maskless on Commercial Flight - From Fox News