Trending on twitter: Airplane dress code

A woman flying from Las Vegas on Southwest this spring says she was confronted by an airline employee for showing too much cleavage. In another recent case, an American Airlines pilot lectured a passenger because her T-shirt bore a four-letter expletive. She was allowed to keep flying after draping a shawl over the shirt.

Both women told their stories to sympathetic bloggers, and the debate over what you can wear in the air went viral.

It's not always clear what's appropriate. Airlines don't publish dress codes. There are no rules that spell out the highest hemline or the lowest neckline allowed. That can leave passengers guessing how far to push fashion boundaries. Every once in a while the airline says: Not that far.

"It's like any service business. If you run a family restaurant and somebody is swearing, you kindly ask them to leave," says Kenneth Quinn, an aviation lawyer and former chief counsel at the U.S. Federal Aviation Administration.

The American Airlines passenger, who declined to be interviewed by The Associated Press, works for an abortion provider. Supporters suggested that she was singled out because her T-shirt had a pro-choice slogan.

A spokesman for American says the passenger was asked to cover up "because of the F-word on the T-shirt." He says that the airline isn't taking sides in the abortion debate.

Last week, Arijit Guha, a graduate student at Arizona State University, was barred from a Delta flight in Buffalo, N.Y., because of a T-shirt that mocked federal security agents and included the words, "Terrists gonna kill us all." He says the misspelled shirt was satirical and he wore it to protest what he considers racial profiling.

"I thought it was a very American idea to speak up and dissent when you think people's rights are being violated," Guha says. The pilot thought it scared other passengers.

American and Delta are within their rights to make the passengers change shirts even if messages are political, says Joe Larsen, a First Amendment lawyer from Houston who has defended many media companies.

The First Amendment prohibits government from limiting a person's free-speech rights, but it doesn't apply to rules set by private companies, Larsen says. He notes that government security screeners didn't challenge Guha; private Delta employees did.

In short, since airlines and their planes are private property and not a public space like the courthouse steps, crews can tell you what to wear.