American Airlines is reviewing an incident in which Sen. Ted Cruz was photographed on one of its flights without a mask, Fox News has learned.

The Texas Republican was flying Sunday via one of American's domestic regional partners, American Airlines told Fox News.

“For the well-being of our customers and team members, we require face coverings to be worn onboard, and we expect our customers to comply with our policies when they choose to travel with us," the airline said in a statement to Fox News. "As we do in all instances like these, we reviewed the details of the matter, and while our policy does not apply while eating or drinking, we have reached out to Sen. Cruz to affirm the importance of this policy as part of our commitment to protecting the health and safety of the traveling public.”

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Hosseh Enad, a Democratic Congressional Committee operative, tweeted a photo showing Cruz seated aboard a plane without a mask.

"Captured today at 10:45am — @TedCruz on a commercial flight, refusing to wear a mask," the tweet read.

A Cruz spokesperson said the senator was drinking coffee at the time his mask was off. He appeared to be holding a beverage and cell phone when the image was taken.

"To help promote safety, Senator Cruz wears a mask when traveling, and practices social distancing where possible. Consistent with airline policy, he temporarily removes the mask while eating or drinking,” a Cruz spokesperson told The Hill.

Another tweet featured an image of Cruz wearing a mask, which read: "SPOTTED: Ted Cruz wearing a mask on a plane when he isn't drinking coffee."

In response to the tweet, Enad also tweeted another image of Cruz maskless while sitting outside the gate to board the flight. It was not clear which airport he was in.

"For those trying to argue that he was drinking, it's not hard to have a mask on and undo one side to take a sip then put it back on," the post read. "Most people take their time drinking coffee. Also, here's a photo of him sitting outside the gate:"

Cruz's office did not respond to a Fox News request for comment.

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American requires the wearing of face coverings while onboard flights. The policy doesn't apply when eating or drinking, the airline said.

In June, several airlines began enforcing rules requiring passengers to wear face masks while traveling as the coronavirus made a resurgence across the United States. Customers who refuse to comply can be denied boarding, according to American.