Southwest Airlines' Facebook promotion was supposed to offer passengers half-price fares. Instead it ended up charging some passengers up to 20 times for a single flight.

Southwest Airlines' Facebook promotion was supposed to offer passengers half-price fares. Instead it ended up charging some passengers up to 20 times for a single flight. Photo: AP

US carrier Southwest Airlines' attempt to thank Facebook friends with a half-price ticket sale has backfired, with customers inadvertently billed multiple times for a single flight - they're not feeling the "luv".

"No, it wasn't a hack. It was just a technology glitch in our system that caused that," duplicate bookings and billings to customers' debit and credit cards, said Southwest spokeswoman Ashley Dillon.

The company became aware of the problem on Friday, when it experienced website slowdowns and saw customers were having to repeatedly refresh pages to take advantage of the airlines' one-day "luv2like" promotion.

The sale designed to celebrate Southwest's reaching the three million mark in Facebook fans was supposed to give customers who booked flights on Friday a 50 per cent discount on certain fares.

Instead, hundreds of frustrated would-be flyers wound up posting stories on Facebook about how their credit and debit cards were being repeatedly charged, in some cases 20 or more times for a single flight.

They tweeted and blogged about the related financial hassles, which ranged from drained checking accounts and bounced cheques to overdrawn credit limits and cancelled bank cards.

Several complained of having to wait hours on the phone when they called to speak to customer service representatives on Friday and Saturday.

Suzanne Worrrell, 37, of Virginia Beach said she was just trying to fly down to Georgia to see her dad on a $US69.60 ($A66.80) ticket but was charged 20 times.

She clicked "purchase the ticket" and Southwest's website froze so she wasn't sure if it went through.

Since she didn't get a verifying email, Worrell said she went to her credit card's website and that's when she noticed repeated charges piling up.

The airline's phone number was busy and she said its website made no mention of the mix-up, but when she got on Facebook she learned she was not alone.

"They've charged over $US1400 ($A1345) now for a $69 ticket," Worrell said. "Initially I was sympathetic. I get it. Stuff happens. Make it better."

Her attitude changed after finally speaking to a Southwest representative on Saturday. She said she was told it will take eight to 10 days before she can get her money back.

AP