By Joanna Plucinska, Toby Sterling and Rajesh Kumar Singh

LONDON Airlines around the world are facing scrutiny from advertising and consumer agencies, regulators, and courts over allegedly making misleading claims about their sustainability efforts, sometimes dubbed "greenwashing".

While a civil suit lodged against KLM in the Netherlands is one of the most prominent, complaints and cases against other airlines have been mounting.

Here are some other recent examples:

ADVERTISING AUTHORITIES

Ryanair, Lufthansa and Etihad have all faced criticism from Britain's advertising watchdog for either alleged instances of oversimplifying or providing misleading environmental claims.

Whether it was Ryanair calling itself Europe's "lowest emission airline" or Lufthansa saying it was "protecting the future" or Etihad referring to "sustainable aviation", the airlines were told to avoid wording that could imply their activities were good for the environment.

"One of the things we just caught onto was that a lot of airlines are making claims about sustainability and eco-friendly, sustainable choices, greener choices," said Miles Lockwood, the director of complaints and investigations at Britain's Advertising Standards Authority (ASA).

But "air travel is one of the most significant (carbon) contributors that consumers make every year."

Ryanair told Reuters it provided all of the information requested by relevant authorities for its campaign in 2019 and that it was disappointed and surprised by the ASA's ruling.

"The Lufthansa Group provides fact-based information about the measures the company is taking to make its flight operations more climate friendly," a spokesperson told Reuters, adding it examined incoming complaints carefully.

Etihad said it was disappointed by the ASA's 2022 ruling against it.

Lockwood said the ASA would use machine learning tools to scan online advertising to catch potentially misleading wording.

Separately, the Austrian advertising watchdog told Lufthansa's Austrian Airlines arm last year to stop making claims about a carbon neutral flight using biofuel.

COURTS

Delta Air Lines faces a proposed class action lawsuit in a Los Angeles federal court over advertisements in which it touted itself as "carbon neutral" based on carbon offset purchases.

The lawsuit alleges that carbon offset programmes don't work as advertised and the company misled consumers.

"This lawsuit is without legal merit," a Delta spokesperson told Reuters, adding the company was working towards a zero emissions goal by 2050 and had moved away from carbon offsets.

The company is investing in newer planes and sustainable fuel to "decarbonise" its operations, the person added.

(Reporting by Joanna Plucinska; Editing by Mark Potter)