Campaigners supporting groups from 17 countries, including Greenpeace, Extinction Rebellion, and Stay Grounded, surrounded jets being exhibited at the annual European Business Aviation Convention & Exhibition (EBACE) at the Geneva airport, with some chaining themselves to aircraft gangways and the exhibition entrance.

The protestors also stuck tobacco-style health warning labels onto planes being shown at the fair, with the giant stickers warning onlookers that private jets “burn our future,” “kill our planet,” and “fuel inequality.”

Klara Maria Schenk, transport campaigner for Greenpeace’s Mobility for All campaign, told Fortune in a phone call on Tuesday that the activists taking part in Tuesday’s demonstration believed private aviation—which she labeled the “utmost unequal [method] of transportation”—was damaging the climate and social equality. She called on lawmakers to act to rein in emissions from private flights.

“For over 20 years, Europe’s super-rich have popped champagne behind closed doors at EBACE while shopping for the latest toxic private jets,” she said. “Sales of private jets are skyrocketing, and with them the one percent’s hugely unfair contribution to the climate crisis—while the most vulnerable people deal with the damage.”

Speaking to Fortune from EBACE in Geneva, Cordula Markert, a spokesperson from Scientist Rebellion Germany, explained why her campaign group—which is comprised of scientists fighting to reduce the impacts of climate change—was taking part in Tuesday’s protest.

“As scientists, we like to look at complex systems like climate and find viable solutions,” she said. “Private jets are like the low-hanging fruit—only one percent of the people in the world are responsible for 50% of the emissions from aviation, and we want to target this one percent.”

She argued that it is “no longer tolerable that the super-rich keeps buying and flying in their private jets for their own benefit, [knowing] that this fuels the flames of climate breakdown.”  

Meanwhile, Mira Kapfinger, a campaigner from the organization Stay Grounded, said in a statement that politicians needed to enforce “fair climate solutions” that included clamping down on frequent fliers.

“Whilst many can’t afford food and rent anymore, the super-rich wreck our planet, unless we put an end to it,” she said. “Apart from banning private jets, it’s also time to end air miles schemes which reward frequent flying, and instead tax frequent flyers.”

Event organizers respond

Ed Bolen, president and CEO of the U.S.-based National Business Aviation Association (NBAA), and Juergen Wiese, chairman of the European Business Aviation Association (EBAA), which co-organized EBACE 2023, said in a statement that the demonstrations were “a completely unacceptable form of protest.”

“We condemn the action, and the threat it has posed to the safety and security of exhibiting companies and EBACE attendees, and others at Geneva Airport,” they said.

They added that the private aviation sector was “deeply committed to climate action.”

“This is an industry that has cut its carbon emissions by 40% over the past 40 years, is continually reducing emissions today, and is collectively focused on achieving net-zero emissions by 2050,” they said. “We as an industry are open to constructive dialogue about the industry’s sustainability leadership, and we regret the protestors’ unfortunate decision to disregard an opportunity for that dialogue to take place.”

Greenpeace’s Schenk told Fortune that the activists on the ground at EBACE had been careful not to disrupt any security at the airport, and had been in touch with security personnel to discuss their intentions.  

Representatives for Geneva airport did not respond to Fortune’s request for comment.

EBACE 2023, which kicked off on Tuesday and will run through Thursday, will have over 10,500 attendees—around half of whom own or operate an aircraft.

The conference, the flagship annual event for Europe’s business jet sector, is making attempts this year to focus on sustainability, with discussion on topics such as electric vertical takeoff and landing aircraft and green aviation fuel.

Tuesday’s protests followed a series of previous demonstrations against private jets in Europe, including a rally at Amsterdam Schiphol airport in November that saw private planes grounded for more than six hours.

Private jet emissions

Private jet usage has come under scrutiny in recent years, with politicians and celebrities increasingly coming under fire for taking highly polluting private flights.

A report from the Patriotic Millionaires and the Institute for Policy Studies earlier this month said that private jet sales were likely to reach their highest level ever this year, with the global fleet more than doubling over the past two decades.  

In a single hour, a private jet can emit two tons of carbon dioxide, according to findings from clean transport campaign group Transport & Environment. Meanwhile, the average person in the EU emits 8.2 tons of CO2 over an entire year.

That means private jet passengers emit up to 14 times more carbon than commercial plane passengers, with private planes up to 50 times more polluting than trains.

Earlier this year, a study by Greenpeace found that the number of private jet flights had risen by 64% in Europe in 2022.

The research also found that the carbon emitted by private jets last year surpassed the amount emitted by Uganda, a country with a population of almost 46 million.