Britain’s advertising watchdog ordered Ryanair Holdings Plc to stop showing “misleading” ads that claim the discounter is Europe’s lowest-emissions carrier.

The Advertising Standards Authority found that TV, radio and newspaper promos made assertions regarding Ryanair’s carbon-emissions ranking that were unsubstantiated and based partly on old data, saying they must not appear again in their current form.

Ryanair said in an email it provided information to support its case and that the ads have provided a “hugely important message” for customers in 10 European countries. The Dublin-based company based its claims on its young, fuel-efficient fleet, and on having occupancy levels that are generally the highest in Europe.

Airlines are facing increasing pressure over their CO2 record, with a sector that produced 2.4% of all human-induced emissions in 2018 set to become the single biggest producer by 2050 if other industries cut their output more quickly, according to some projections. Ryanair finds itself in the firing line because of a business model that has opened up hundreds of routes to mass travel. It hit back with its first environmentally focused advertising campaign in September.

The ASA found that it was reasonable for the carrier to express its carbon footprint as grams of CO2 produced per passenger per mile.

At the same time, Ryanair’s assertions relied on calculations regarding seating density that weren’t explained, and in one press ad it claimed to have the best emissions record of any “major” European airline when the comparison was with only four other carriers. One survey that ranked the company top for efficiency was dated to 2011, while another placed it fifth.

“Ryanair should stop green-washing and start doing something to tackle its sky-high emissions,” said Jo Dardenne, aviation manager at lobby group Transport & Environment.

T&E called on governments to reach bilateral accords on taxing jet fuel while the European Union works on plans for a region-wide levy.