Adds Frontier declining comment, Spirit not immediately comment, more details from letter in paragraphs 3-11

By David Shepardson

WASHINGTON, Jan 22 (Reuters) - Three U.S. senators said they want Frontier Airlines ULCC.O and Spirit Airlines SAVEQ.PK to disclose whether they are manipulating seat fees by using customers' personal information to charge different fees to passengers on the same flight.

Senators Maggie Hassan, Josh Hawley and Richard Blumenthal cited on Wednesday the carriers' decision to ask for personal information before revealing seat fees, adding the airlines were apparently "using customers' personal information to charge different seat fees to passengers on the same flight" despite having the same fare. The senators said the carriers could be using consumers' ZIP codes, search history or other information "to influence pricing."

In a letter, they called on the airlines to stop collecting personal information before showing fees, saying it undermines consumers' confidence, reduces competition and prevents customers from accurately comparing prices."

Frontier declined to comment. Spirit did not respond to a request for comment. The senators also wrote to Amadeus-owned AMA.MC software firm Navitaire asking if the airlines had asked it collect data and use it in their pricing algorithms. The company did not immediately comment.

Last month, the bipartisan group of senators took part in a hearing that harshly criticized rising airline fees for luggage and seat assignments, calling the fees unfair and noting how different customers are charged differently.

"This is Russian roulette," Hawley said. "Nobody enjoys flying on your airlines. It's a disaster. ... It's absolutely terrible."

A report disclosed that five U.S. airlines, including Frontier and Spirit, collectively earned $12.4 billion in revenue from seat fees between 2018 and 2023.

Airlines say the fees are about customer choice but acknowledge the charges are a key part of their revenue structure as they face rising costs.

A year-long investigation by Blumenthal's panel found that carriers are increasingly using algorithms to set fees.

Frontier and Spirit paid $26 million to gate agents and others between 2022 and 2023 to catch passengers not paying the airline's required bag fees or having oversized items, the committee said.

Last year, U.S. airlines sued to block the U.S. Transportation Department's new rule on upfront fee disclosure.

(Reporting by David Shepardson; Editing by Jamie Freed)

((David.Shepardson@thomsonreuters.com; 2028988324;))