The European Union is looking into several carriers over allegations they can’t back their carbon offsetting programs with actual scientific data.

Numerous European carriers are being investigated by the European Union on the claims their carbon offsetting programs may be nothing more than “greenwashing.”

Reuters reports some of the airlines receiving investigation letters include the carriers under Lufthansa Group, Air France KLM, Norwegian Air, and SAS.

EU Seeks Scientific Proof Airlines are Offsetting Emissions

Under Lufthansa group alone, the airlines in question include Brussels Airlines, Lufthansa, SWISS, Austrian Airlines, and Eurowings. However, up to 17 airlines could be under investigation according to a letter sent by the European Consumer Organisation. Other carriers named in the letter to the EU include Finnair, TAP Portugal Airlines, and Vueling. None of those airlines have publicly commented about receiving a letter from the EU about their environmental programs.

The probe seeks to find out information about the airlines’ evidence that their carbon emissions offsetting programs are working to reduce CO2 exhausted from aircraft. Collectively, airlines have taken many different approaches to offsetting emissions, ranging from climate projects including planting trees, to using biofuels. In 2017, KLM Royal Dutch Airlines outlined how using recyclable materials and flying with less weight resulted in lower emissions.

While the investigation is in the starting phase, aviation consortium Airlines for Europe say international regulations are still being developed and may differ between European nations. In a statement posted on LinkedIn, the organization says they are still on track to achieve net zero emissions by 2050 and are concerned about some of the allegations raised by the EU.

“We are particularly concerned about the remarks on Sustainable Aviation Fuel (SAF) and the requirement for a clear justification of their environmental impact,” the statement reads. “The EU has implemented an ambitious SAF mandate, supported and endorsed by the European Commission, and the science supports that this is a more sustainable alternative to regular jet fuel.”

In their sustainability pledge, the group notes: “There is no panacea for reducing greenhouse gas emissions; the solutions will vary with geography, economics, and demand.” However, the collective plan is to use technology and activity to achieve net zero status.

While Lufthansa, Air France KLM, and SAS confirmed they received letters from the EU, Norwegian told Reuters they were “working to familiarize ourselves with the case material and will answer within the deadline.”