Travelers may be denied boarding if their passport does not meet a specific requirement. A strict rule applies to passports, which must not break a certain condition before flying.

This rule is referred to as the "six-month rule". Further information about this rule and its implications can be found through Secret Chicago.

Details about the rule and how it affects travelers are available, but the key point is that passports must comply with this requirement to avoid being turned away at airports such as O'Hare or Midway.