United-Continental and US Airways have joined Delta in adding a $3 surcharge to one-way tickets to Europe, days after the European Union started requiring airlines to pay for carbon emissions.

Spokesmen for all three airlines would not discuss the reasons for the surcharges.

But industry analysts call the surcharge a clear sign that consumers could bear the brunt of a European law that the U.S. airline industry has estimated would cost it $3.1 billion from now through 2020.

The new surcharge also happens as consumers are already paying surcharges for higher fuel costs on international flights.

“This is a new fee, so it’s going to go straight to the bottom line, and that means consumers will be paying,” says Charles Leocha, director of the Consumer Travel Alliance. “This is one more fee on top of all the other ones, so it adds up.”

Under the European Union’s Emissions Trading Scheme to combat global climate change, various industries have had to pay for their carbon emissions for years. But on Jan. 1, airlines flying in and out of the European Union were included in the program for the first time.

The program sets a cap on carbon-dioxide emissions and allows airlines to fly 85% of that cap for free through this year. That percentage decreases after 2013. Airlines have to pay for the rest by buying “allowances” from industries that burn less.

Airlines that don’t fly with the proper number of allowances could incur a fine of up to $130 per ton of carbon-dioxide emissions and risk being barred from European airspace.

READ MORE: USA TODAY