Have you looked at their current pay rates lately? A 20% raise would put them right in line with the new pattern that has been established by Alaska and JetBlue. The new pattern is right around $180/hr for SNB rates, and WB rates in the $210/hr range by end of contract. You can reasonably demand an extra few percent in the name of pattern bargaining (jacking up the house one corner at a time), but you can't expect the NMB to allow a demand for 36% raises when 20% would put you in range of the established bargaining pattern.
Maybe I missed something but JB max pay is $159/hr and Alaska's is $172.