Southwest has been sued by a search engine that the airline says breached its terms by displaying cheap flights

• Skiplagged sued Southwest, seeking a judgement on whether it violated the airline's terms.
• The lawsuit came after Southwest sued Kiwi.com, another flight-info site, in Texas.
• Southwest sent letters threatening legal action over fare listings, Skiplagged's complaint said.

Skiplagged, a flight-information website, asked a New York court to rule on whether it was breaking Southwest Airline's terms of service by posting flight airfares.

"Skiplagged does not access Southwest.com or use the Southwest API to obtain data published on Skiplagged.com," the tech company said in its complaint, "and is not bound by the Southwest terms and conditions."

The filing was curious in that Southwest hadn't publicly accused Skiplagged of breaking its terms and services. The filing was instead an indirect response to another lawsuit where Southwest was suing a different online travel agency, although Skiplagged wasn't named as a defendant.

Since January, Southwest has been in a legal battle with Kiwi.com in federal court in Texas. Southwest in that lawsuit sought an injunction to stop Kiwi.com from displaying its flights. The airline has stated that it doesn't allow online travel agencies to sell its flights without written permission.

"Kiwi knowingly and intentionally targets the Southwest website to harvest Southwest's fare and pricing information for its own commercial benefit and without Southwest's authorization," the airline said in its complaint.

Seeing the threat posed by the Texas lawsuit, Skiplagged decided to sue Southwest in New York, its home state, in a pre-emptive legal move. The complaint didn't say Skiplagged's data came from.

Skiplagged, speaking through its lawyer, Irwin B. Schwartz, of BLA Schwartz PC, declined to comment. A Southwest spokesperson also declined to comment. Kiwi.com didn't respond to a request for comment.

The Skiplagged lawsuit followed a volley of private letters between Southwest and Skiplagged this year, according to the complaint. Both companies declined a request to share the letters but Skiplagged's complaint described a communication from Southwest as "threatening."

In two letters in early June, Southwest accused Skiplagged of "unlawfully 'web scraping' data from Southwest.com," among other complaints, according to a court filing.

A few days later, Skiplagged sent its own letter, telling Southwest it didn't scrape data from the airline's website.

By early July, Southwest had responded with escalating claims, telling Skiplagged that it was "inducing Kiwi.com to breach Southwest's website" by linking to that site, according to the complaint.