Here is what the ALPA By-Laws State, and based upon this wording, a change in scope would be grounds for MEMRAT:
SECTION 2 - RATIFICATION
A. Any contract, letter of agreement or letter of understanding that, in the opinion of the MEC,
substantially affects the pay, working conditions, retirement, or career security of member pilots will
be subject to membership ratification under the following terms and conditions:
(1) The MEC will, at its option, ballot the membership of their airline to determine if it is their
desire to have membership ratification. Once membership ratification is established it will remain
in effect until changed by another ballot of the membership through MEC action.
Of course the answer is in the MEC policy manual and I do not know if I can download that document.