In 1998 the Department of Transportation decided airlines needed some help figuring out how to give passengers tiny bags of peanuts. The department's Aviation Enforcement Office sent an unsolicited letter to the airlines suggesting that they provide peanut-free buffer zones for all passengers with medically documented severe peanut allergies.
Congress responded with overwhelming force, first threatening to cut off funding to the office that sent the letter and subsequently banning the use of government funds to give legume-related advice "until 90 days after submission to the Congress of a peer-reviewed scientific study that determined that there are severe reactions by passengers to peanuts as a result of contact with very small airborne peanut particles of the kind that passengers might encounter in an aircraft."
Since then, a number of airlines have started offering peanut-free flights of their own accord, in deference to fliers with allergies, particularly children. But Elizabeth Goldenberg, a Canadian lawyer and mother of a child who is allergic to peanuts, won't rest until every flight is completely nut-free. In July she filed a request with the Department of Transportation asking that peanuts be banned from all U.S. flights.
In her petition letter, Goldenberg argues that "it makes business sense to ban peanuts from airplanes," somewhat overenthusiastically calculating the "'ripple effect' of food allergy" at "18,351,620 potential lost sales representing almost 6 percent of the US population." The airlines that have already switched to pretzels clearly see Goldenberg's side of the argument. As for the rest, they're safe from peanut regulation for now. That peer-reviewed study has yet to materialize, so peanuts retain their special protected status for now.