Passengers flying with Jet2, Ryanair, TUI, and easyJet could be turned away at the gate this summer if they fall foul of the airlines' dress codes. An industry insider has shed light on the strict 'outfit' rule that might see holidaymakers barred from boarding their flights.

Mary Jo Manzanares, who has a wealth of experience as a travel writer and former flight attendant spanning 33 years, spoke to CNN Travel about why certain clothing choices can lead to passengers being refused entry onto their eagerly anticipated flights.

In her discussion with CNN Travel, Manzanares explained: "You've got to make your priority resolving things on the ground, making sure that there is no aggression. When you go to 30,000ft, you may have passenger conversation or banter or inappropriate comments between passengers, add in a little alcohol, and you may be making an unscheduled landing. And no-one wants that."

A flight attendant also voiced concerns to The Sun, stating: "We're well within our rights to prevent people getting on the flight and it's used frequently for people who aren't dressed in a way we would deem to be acceptable."

The warning to travellers planning to fly with Jet2, Ryanair, TUI, and Easyjet was clear as they added: "There are some obvious examples here, including t-shirts with swear words or offensive logos on them, which people are regularly asked to cover up, or remove, before they get on board," reports Birmingham Live.

While most airlines don't provide official dress code guidelines, it's generally a good idea to avoid wearing dirty or torn clothes, overly casual outfits, or any clothing with potentially offensive slogans or rude language. While some airlines are fine with passengers wearing flip-flops, others may not allow 'beach attire' on board.

It's also important to note that if a country has specific laws or local customs regarding clothing, airlines may expect passengers to respect these rules before boarding.