The PDP caucus led by Senator Ahmed Makarfi accused the APC of collaborating with INEC and security operatives to rob Ize-Iyamu of his mandate.
The Independent National Electoral Commission (INEC) had declared Obaseki of the All Progressives Congress winner of the election having polled 319,483 votes as against PDP's Osagie Ize-Iyamu, who had 253,173 votes.
The PDP caucus led by Senator Ahmed Makarfi, however, rejected the outcome of the election, calling on its members in Edo to remain resilient.
According to the head of PDP publicity division for national publicity secretary, Adm. Chinwe Nnorom, the decision to reject the election outcome was made at a meeting of the party's executives and was unanimous.
Nnorom said: "The National Caucus frowned at the brazen display of avarice and desperation against the Edo electorates and democracy on September 28 and 29, 2016 by the ruling APC in collaboration with INEC and security agencies all in the name of Governorship Election.
"Consequently, the Meeting unanimously rejected the outcome of the charade that took place in Edo State.
"Finally, the National Caucus calls on all our Party members nationwide and in Edo State in particular to remain calm and resilient in the face of this daylight robbery of their mandate to our Candidate, Pastor Osagie Ize-Iyamu. We believe that justice will be served."
In attendance at the meeting were the Deputy Senate President, Senator Ike Ekweremadu, the Chairman of the Board of Trustees (BoT), Senator Walid Jubrin, Principal Officers of the National Assembly, Governors of Ondo, Taraba, Bayelsa, Gombe, other members of the National Caretaker Committee, National Vice Chairmen, former Governors, former Ministers, other members of BoT and other members of the National Executive Committee (NEC).