Many countries, including the U.S., have a departure or arrival tax that people leaving or arriving to the country BY AIR pay. This tax is partially used for maintaining airports, but a portion also goes to the federal government.
In some countries this tax is included in the cost of airline tickets (e.g., the U.S.), and in some it is paid separately (e.g., Costa Rica). The U.S. departure/arrival taxes are currently $13.40 each way. Smaller countries with smaller infrastructures charge more than this.
In 2012, 61,149,684 international visitors came to the U.S. Raising the departure and arrival taxes to $30 per person each way would generate more than $1 BILLION additional dollars for the U.S. economy, from international travelers who can afford it, something both parties should favor.