Most airlines offer impressive travel perks to its employees including discounted last-minute flights for family and friends. It’s one of the most attractive benefits of working for a commercial airline. However, United Airlines has recently fired 35 employees for abusing these perks in a so called “brokering scheme” involving the sale of employee travel privileges.

“Enjoying flying privileges is a unique and special advantage of working at an airline, and it is intended only for our employees and their friends and family. We have clear rules on flying privileges so we can all fairly enjoy this benefit,” the airline said in a statement Thursday.

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The scheme was uncovered when nine travelers where heading overseas using passes from United employees whose names they were not able to provide at check-in. United said the passengers reported paying $3,500 to $4,000 per person for a year’s worth of travel.

In an email sent to United Airline employees on Wednesday, it was noted that the fired employees had listed false relatives or had given their passes away thinking they were going to a co-worker’s friend or relative. Both infractions are against the airline’s travel benefits program rules. 

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According to the Chicago Tribune, the abuse of airline perks by employees is not a rare occurrence and schemes being advertised as “deals” can be found across the internet. The news website sited a recent Chicago-based Craigslist ad posted by a Delta Airlines employee selling a year’s worth of travel for $2,000.

It remains to be seen if this recent event will force airlines to impart stricter guidelines on their benefits programs. In the meantime, employees will probably be paying much closer attention to the current rules.