What is this “ZP” tax on my airline ticket for?

ZP is the code for “Passenger Segment Fee”. This is a fee, currently $4.00, on each segment of your flight. There is no cap on the number of segments that can be taxed. Several years ago, the feds lowered the excise tax on airline tickets from 10% to 7.5% and added this “Passenger Segment Fee” so that taxes were distributed a little more evenly between cheaper and more expensive tickets. This tax is collected by the IRS and goes towards funding the Federal Aviation Administration (FAA) and the Airport Improvement Program.