11:37 AM PT -- Kattan's attorney, Samuel Joshua Smith, tells us, "We strongly deny that Mr. Kattan would ever refuse to wear a mask. Mr. Kattan is fully vaccinated and unequivocally supports CDC guidelines."
He continues, "This past Monday Mr. Kattan was returning to Los Angeles from a successful tour of comedy shows. Unfortunately, Mr. Kattan suffered a strong allergic reaction to supplements he has been taking to treat lingering neck pain from his injury on SNL. This reaction affected his balance and psychological state. The effects also caused him to have trouble breathing."
Smith finishes with, "Mr. Kattan sends a warning out to all his fans suffering through back and neck injury... “apparently, not all supplements are created equally!”
Smith says Kattan was able to get on the next plane home.
Chris Kattan allegedly pulled an anti-masker moment onboard an American Airlines flight, frightening other passengers and prompting airline staff to order him off the plane ... TMZ has learned.
Sources with direct knowledge tell us ... the ex-'SNL' star had boarded the flight Monday from Dallas/Fort Worth to LAX, but his appearance startled several passengers who were seated near him in first class.
We're told Chris was stumbling and seemed sick, at least to other passengers ... partially because he had mucous hanging out of his nose when he leaned over. He was not wearing a mask at that point, and we're told passengers alerted flight attendants ... who brought him paper towels and ordered him to put on a mask.
We're told Chris did put one on -- the federal mask mandate is still in effect for air travel -- but left it below his nose ... and by now his behavior had other passengers on edge. Witnesses say he begged flight attendants not to boot him, and even asked if they'd seen him on 'SNL.'
Staffers asked him multiple times to pull up his mask, and warned if he didn't do it immediately their next call would be to the cops. At that point, he finally got up and left.
We've made calls to Kattan's team to get his side of the story, but so far ... no word back.