Westjet has the shortest seat pitch among any Canadian airline - the distance from one seat to the next.
Sections of WJ now 28 inches.
Smallest on Flair, AC is 29 inches.
Westjet execs called the space "acceptable", when trying it out.
"WestJet pilots believe this reconfiguration erodes the guest experience and devalues our brand," said Jacob Astin, who chairs the WestJet contingent of the Air Line Pilots Association, in an emailed statement.
He noted that Transport Canada had approved the change, but said it nonetheless "reduces the superior safety margins of previous layouts due to increased cramping."