The integrity of the vote that installed Bill Shorten as federal Labor leader is under scrutiny after an ALP tribunal found the mailing addresses for dozens of ballot papers were altered at the request of a staff member of senator Sam Dastyari.

The mailing addresses of at least 20 ALP members were changed to the home address or post office box of disgraced Auburn councillor Hicham Zraika, who has been suspended from the Labor party for six months after branch stacking charges were brought against him.

Senator Sam Dastyari's former employee Michael Buckland asked for ALP members' addresses to be altered. Credit:Alex Ellinghausen

A tribunal decision obtained by Fairfax Media says changes to the addresses of 50 members were authorised by NSW Labor Right assistant secretary Kaila Murnain at the request of Michael Buckland - a former Young Labor president who at the time worked for Senator Dastyari.

The tribunal found Cr Zraika should have alerted the party when he received the 20 ballot papers destined for other party members.