Since March 1, 2010, all U.S. citizens including minors have been required to present a valid passport or passport card for travel into Mexico. While documents are not routinely checked along the land border, Mexican authorities at immigration checkpoints approximately 20 to 30 kilometers from the border with the U.S. will often conduct vehicle and document inspections and will require valid travel documents and an entry permit or Forma Migratoria Multiple (FMM). All U.S. citizens entering by land and traveling farther than 20 kilometers into Mexico should stop at an immigration checkpoint to obtain an FMM, even if not explicitly directed to do so by Mexican officials. Beyond the 20-30 kilometer border zone, all non-Mexican citizens must have valid immigration documents (FMM, FM2, FM3 or FME) regardless of the original place of entry. Failure to present an FMM when checking in for an international flight departing Mexico can result in delays or missed flights as airlines may insist that a valid FMM be obtained from Mexican immigration authorities (Instituto Nacional de Migración, INM) before issuing a boarding pass.