Plus sized model Juliana Nehme, 38, said Doha-based airline Qatar Airways discriminated against her due to her size in a social media video, which has since gone viral.
Ms Nehme was travelling with her mum, sister and nephew after holidaying in Lebanon and was on her way back home to Brazil, via Doha.
She claims a staffer told her she would need to buy a first-class seat - which was significantly more expensive - if she wanted to board the flight home.
The airline reportedly claimed the plus-sized influencer was barred from flying because one of Ms Nehme's relatives didn't produce a required Covid-19 test.
A Qatar Airlines spokesperson told the Daily Mail: “The passenger in question at Beirut Airport was initially extremely rude and aggressive to check-in staff when one of her traveling party did not produce required PCR documentation for entry to Brazil.
“As a result, airport security was requested to intervene as staff and passengers were extremely concerned with her behavior.”
Ms Nehme's clip - which she shared on Thursday - has already racked up 50,000 likes and thousands of comments.
She said there were no similar issues while boarding a connecting Air France flight to Lebanon - where the family had been on holiday.
Speaking in her native Portuguese, she said: “I bought a return ticket to Brazil through Qatar and arriving at the time to check in, a Qatar flight attendant called my mother while another staffer was finishing our check-in, and told her I wasn’t welcome to board because I’m fat.”
Ms Nehme said she had already forked out $4,000 (£3,310) on economy seats.
This included her personal $947 (£784) ticket, "only to be denied from boarding the flight".
Juliana said Qatar Airways did not offer to refund her the money she had paid for her ticket.
Instead, the influencer claimed, the airline said she needed to buy a first-class ticket for USD 3,000 (GBP 2,480) so she could fit into the seat.
She explained: “A Qatar airline (staffer) called my mother while the lady was finishing our check-in and told her that I wasn’t welcome to board because I’m fat and they weren’t going to welcome me on the flight!”
Qatar Airways outlined its policy regarding larger passengers to the Daily Mail.
"[Anyone] who impedes upon the space of a fellow traveller and cannot secure their seatbelt or lower their armrests may be required to purchase an additional seat both as a safety precaution and for the comfort and safety of all passengers."
The airline claimed this was in line with industry practice.
At the time of reporting, Juliana remained in Lebanon unable to get back home and Qatar Airways had not responded to her allegations.
Qatar Airways was named the world's best airline at the 2022 Skytrax World Airline Awards.