14 CFR §382.159

1. (a)Any person believing that a carrier has violated any provision of this part may seek assistance or file an informal complaint at the Department of Transportation no later than 6 months after the date of the incident by either:
   1. (1)Going to the web site of the Department's Aviation Consumer Protection Division at http://airconsumer.ost.dot.gov and selecting “Air Travel Problems and Complaints,” or
   2. (2)Writing to Department of Transportation, Aviation Consumer Protection Division (C-75), 1200 New Jersey Avenue, SE., Washington, DC 20590.
2. (b)Any person believing that a carrier has violated any provision of this part may also file a formal complaint under the applicable procedures of 14 CFR part 302.
3. (c)You must file a formal complaint under this part within six months of the incident on which the complaint is based in order to ensure that the Department of Transportation will investigate the matter.