A consumer complaint filed with the EU's executive arm alleges that the 17 firms are Greenwashing, the practices of making misleading climate-related claims.
BEUC said the airline claims violated EU regulations on unfair commercial practices.
The BEUC urged authorities to take the matter into their hands and crack down on this greenwashing practice seriously misleading consumers, BEUC deputy director general Ursula Pachl said in a statement.
Airlines must stop giving consumers the false impression that they are choosing a sustainable transport mode, Pachl said.
Greenwashing is when companies utilize deceptive promises to convince the public that their products or operations are eco-friendly.
The BEUC said airlines are misleading consumers by charging them more for contributing to the development of sustainable aircraft fuels SAF, which are not market-ready and will only represent a minor portion of a plane's fuel mix once they become widely available.
The environmental group also denounced claims that paying extra credits can offset or compensate for a flight's CO 2 emissions.
A Air France-KLM spokesman said the Franco-Dutch group was paying increased attention to the precision of these messages and that it was the world's biggest consumer of sustainable aviation fuels last year.
Germany's Lufthansa said it plans to reduce its net emissions by half by 2030 compared to 2019 levels and has a constant dialogue with customers.