(Reuters) — Environmental groups are suing KLM, the Dutch subsidiary of Air France, over an advertising campaign they allege breaches European consumer law by misleading the public over how sustainable its flights are.

Dutch campaigners Fossielvrij NL, supported by environmental law charity ClientEarth and Reclame Fossielvrij, on Wednesday filed the first lawsuit alleging greenwashing in the airline industry in the District Court of Amsterdam.

KLM, which says it has invested millions of euros in a more sustainable fleet and is working toward the industry goal of net zero carbon emissions by 2050, met with the groups before the suit was filed but failed to find a solution.

“It would certainly not be in our interests to misinform our customers. It’s our responsibility to make future travel as sustainable as possible,” the airline said in a statement sent to Reuters. “We believe that our communications comply with the applicable legislation and regulations.”

Campaigners have launched hundreds of climate change-related suits against companies, governments and authorities to try to accelerate the world's shift to a low-carbon economy and fight an escalating climate crisis. They want to stop KLM’s ‘Fly Responsibly’ advertisements, alleging they violate the Dutch implementation of the EU's Unfair Consumer Practices Directive by giving the false impression its flights will not exacerbate the climate crisis.

KLM launched the advertising campaign last December, urging customers to help pioneer a “sustainable future” for aviation by paying towards reforestation projects or by contributing to the cost of greener aviation fuels through its CO2ZERO offers, designed to help tackle flight-related carbon emissions.

Campaign groups allege that aviation cannot be made sustainable quickly enough to meet global climate goals by replacing fossil jet fuel, improved engines, efficiencies or other future technologies and want a reduction in flights — a view echoed by a leading investor group in March. 

The Dutch court will decide whether the case can proceed before KLM has to file any defense, ClientEarth said.