Raila Odinga's ODM party has rejected Tuesday's delegates victory by former minister Ochillo Ayacko.
Delegates from all eight executive branches had unanimously endorsed Mr. Ayacko, having secured 44 of 49 votes cast.
Through National Elections Board chair Judy Pareno, Raila distanced himself from the decision by delegates.
"Branch chairmen have no powers to conduct nominations on behalf of the party," she said, during an interview with KTN.
Further, the nominated senator preempted planned disciplinary actions against branch chairman Philip Mak'Abong'o.
"Makabong’o is a perennial intruder on electoral matters in Migori county. This time he must be punished," she said.
Ayacko is one of the front runners for ODM ticket ahead of October 8th by-election that was precipitated by the death of Ben Okello.
Also interested in the ticket are Dalmas Otieno, John Pesa and Omondi Anyanga.
On Monday, ODM insisted that the candidate will be hand-picked and gave NEB until 26th July to submit the name of favourite to NEC.
During Okello's funeral, Raila reconciled Ayacko with Governor Okoth Obado in a move seen as a plot to back the former for senatorial seat.