Passengers carrying extra baggage on their bodies will have to pay for an extra seat – if they want to fly the friendly skies.

United Airlines on Wednesday began barring overweight fliers flying out of Chicago who:

– Can’t fit into a single seat in the ticketed cabin.

– Can’t buckle their seatbelt – even using the seatbelt extender.

– Can’t put the armrests down when seated.

Those deemed too fat to fly “must either purchase a ticket for an additional seat, or purchase an upgrade to a cabin with seats that address the above-listed scenarios,” United Airlines wrote on its Web site.

If no other seats are available on that flight, the hefty flier is grounded until two conjoined seats can be found on the next plane out.

“This will apply after all other solutions are exhausted,” United spokeswoman Robin Urbanski Janikowski said. “Should the flight be full, which is rare in today’s economy … we will offer the second seat on another flight at the same fare that was originally paid.”

United received more than 700 complaints last year from travelers who “did not have a comfortable flight because the person next to them infringed on their seat,” she said.

Urbanski Janikowski said eight other U.S. airlines have similar seating policies requiring plus-sized passengers to “purchase a second seat” if they can’t fit into one.

United did not explain who at the airline makes the call. Chicago-based WBBM Newsradio said the airline “instructed its customer service representatives at O’Hare International Airport ticket counters and gates to be extra vigilant.”