Using this as springboard because a bit misunderstood.
IPA Apprentice members are members. Classified as those who are probationary crew members. Protected by the current Collective Bargaining Agreement. Don't pay dues (can't vote), but can work on a Committee and attend meetings. Some disciplinary limitations in Article 7 in first year, but otherwise, from the IPA Constitution and Bylaws:

4. APPRENTICE
a. An Apprentice member is a Crewmember who has not yet completed the required Company probationary period (regular or extended), as stipulated in the UPS/IPA Collective Bargaining Agreement.
b. An Apprentice member shall not be required to pay dues until the beginning of the pay period following the pay period in which he completes his probationary period with the Company.
c. An Apprentice member shall not owe any part of an assessment that is levied prior to the beginning of the pay period following the pay period in which he completes his probationary period with the Company.
d. An Apprentice member shall be responsible for fees and fines.
e. An Apprentice member shall be required to complete and return to the Secretary his Application for Membership and to the Treasurer his Dues Check-off Card and his Initiation Fee Check-off Card;
f. An Apprentice member not in arrears is entitled to General Rights and only the following Participatory Rights:
(1) Attend and participate in GMMs;
(2) Attend open sessions of Executive Board Meetings;
(3) Be a Committee member, if approved by the Executive Board member tasked with oversight.

Bottom Line, Like other member classifications of the IPA, they are technically IPA members.