Effiong announced his decision to leave the PDP on the floor of the senate on Thursday, citing the crisis in the party.
“Over the past one year this party has disintegrated; because of the crisis in the party, I have decided to resign from the PDP and join the APC,” he said.
Reacting to the development, Godswill Akpabio, senate minority leader, said Effiong had automatically lost his seat because he became a senator under the platform of the PDP.
He said the party would go to court challenge the continued state of the lawmaker in the senate.
In November 2016, Omoyele Omogunwa, a senator from Ondo south, had also defected from the PDP to the APC, citing the need to support Rotimi Akeredolu, the governor-elect of his state as the reason for his action.