The airline said the couple became profane after being reprimanded for what actress Leisha Hailey characterized as "one modest kiss.''
Hailey immediately used her Twitter account to accuse the airline of discrimination and call for a boycott.
Hailey is best known for playing Alice Pieszecki in the now defunct Showtime lesbian life drama "The L-Word.''
The incident cast a national media spotlight on the actress, who is now part of the electro-pop duo Uh Huh Her.
Halley's publicist Libby Coffey said the encounter was real and was "absolutely not'' done as a publicity stunt for her band's upcoming breast cancer awareness tour.
Hailey and partner Camila Grey also denied in a statement Tuesday that the affection they showed toward each other was inappropriate.
"We want to make it clear we were not making out or creating any kind of spectacle of ourselves, it was one modest kiss,'' the written statement said. "We are responsible adult women who walk through the world with dignity. We were simply being affectionate like any normal couple.''
The airline responded that Hailey's display of affection was excessive and drew customer complaints, and that the women cursed after being reprimanded.
"Additional reports from our employees and customers onboard Flight 2274 during a stop in El Paso on Sunday now confirm profane language was being used loudly by two passengers,'' the airline said. "Although we have reports of what customers characterize as an excessive public display of affection, ultimately their aggressive reaction led to their removal from the aircraft.''
Hailey and Grey acknowledged that they became upset after the flight attendant reprimanded them and told them Southwest is a family airline.
"We take full responsibility for getting verbally upset with the flight attendant,'' their statement said. "No matter how quietly homophobia is whispered, it doesn't make it any less loud.''
Hailey and Gray said they plan to file a formal complaint with the airline.
Details of how the couple was escorted off the flight were not included in the Southwest statement. Initial reports had the flight going from Baltimore to St. Louis, but a tweet by the band says its members were flying from El Paso, Texas, to Los Angeles, which the airline confirmed.
Hailey said in a tweet that she has an audio and video recording of the encounter between the couple and the flight attendant. It's not immediately clear who made it. Coffey did not respond to an email requesting access to the recordings.
Hailey also demanded a public apology and a refund from the airline. The airline said it had reached out to all passengers involved to offer refunds.