With Europe’s Emissions Trading System extended to the aviation industry as of last week, requiring all airline carriers landing in the 27-nation European Union to monitor their carbon emissions, flights to and from Europe are likely to get steeper.

The BBC reports that each airline is allowed a specified amount of CO2 emissions. If the airline emits more than that amount, it must purchase carbon allowances. If it emits less than its limit, it can sell its extra allowances to other heavy carbon emitters, such as other airlines, steel makers, refineries or power plants. Airlines are saying they will pass along to their customers by raising fares. 

German air carrier Lufthansa, for instance, told the Associated Press that would have to buy at least 35 percent of the certificates it needs based on past emissions and recent growth. It put the cost at $168 million in 2012.

Bloomberg quotes aviation information provider OAG as estimating the total cost to European Union industry at about $4.5 billion.

American carriers already increased fares for European flights last week, though the New York Times reports that the House of Representatives has approved a bill that would bar American air carriers from participating in the system. A similar bill has been introduced in the Senate.