In a rare move, both United Airlines and the Association of Flight Attendants (AFA) have issued statements warning flight attendants to stop trading or choosing flight trips to work on, at risk of dismissal.

According to the airline’s full memo, frustrated staffers have been reporting allegations of "illicit trip brokering" – orchestrated in part through social media – through the last few months, prompting the Chicago-based carrier to launch an internal investigation.

Though flight attendants are lawfully allowed to switch trips with one another to ensure full coverage, according to Fast Company, brokering routes for personal profit is forbidden.

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“Those trades are not the issue. What we're addressing is the growing problem of selecting, trading or parking a pairing to broker, buy or sell it to another Flight Attendant,” the United memo, released March 22, begins.

“Several of the complaints we received pointed out social media posts authored by Flight Attendants that promised ‘hugs,’ ‘kisses,’ ‘candy canes,’ ‘expressions of appreciation’ and other coded enticements in exchange for a pairing,” the message continues. “Our research confirmed this is in fact happening, and these gestures are violations of our policies.”

“We have zero tolerance for this prohibited behavior. When we discover that it's occurring, we will fully investigate and take appropriate action, up to and including discharge,” the notice concludes.

Likewise, the AFA’s memo – released the next day – acknowledges that though flexibility from airlines is essential for a sustainable career in the demanding profession of flight service, brokering flights is unethical and will not be tolerated from the union.

“Understanding that we can’t always control the events in our lives and that our chosen career often makes it necessary for us to adjust our schedules at the last minute, we’ve negotiated industry leading flexibilities to allow us the opportunity to adjust our schedules to achieve that necessary work life balance and to care for our families,” the memo states.

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“However, what has not been negotiated is the increasing parking of pairings with the intent to broker, buy or sell the pairing to another Flight Attendant,” it continues. “Our [joint collective bargaining agreement] includes a provision that expressly prohibits parking. Those individuals who are participating in this activity are creating a disservice to the entire Membership.”

“The time to stop is now,” the notice advises.

As defined by USA Today, a “pairing” can be defined as the parts of a flight journey, while “parking a pairing” is when flight attendants accept trips that they have “no intention of using.”

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When contacted for comment, reps for United returned Fox News’ request for additional comment on the story with the following statement:

“We know schedules are very important to our flight attendants, and we work closely with AFA to make sure our flight attendant scheduling is fair for all of them,” a spokesperson said.

In similar headlines, United fired 35 employees in March in relation to another “brokering scheme” – for the alleged, illicit sale of travel passes to those beyond their immediate family and friends, the Chicago Tribune reported at the time.