Source: Elines

From time to time, we all experience a change or substitution of aircraft that requires a fewer number
of Flight Attendants than was originally scheduled. Our Contract provides for specific procedures to be followed in these circumstances. 

Over the past several weeks, the grounding of the Boeing 737MAX fleet has provided a number of examples many Flight Attendants have experienced when the pairings were originally built as four (4) 
Flight Attendant crew complement pairings. In some instances, the new aircraft assigned to the flight 
required a three (3) Flight Attendant crew complement on the A319/A320 or 737-700

Flight Attendants are reminded to be familiar with what occurs in the event of an aircraft substitution through the Equipment Change language in JCBA Section 7.Q.7.as was previously communicated in the April 3, 2019 E-Lines.