The ruling Peoples' Party of Arunachal (PPA) in a sudden move on Thursday night removed incumbent Pema Khandu and six others for alleged anti-party activities.
The PPA was expected to declare Pario as its leader in the assembly as also the Chief Minister, the sources said.
The PPA temporarily suspended Khandu, his deputy Chowna Mein and five other legislators on disciplinary grounds.
Ordering the suspensions, PPA President Kafia Bengia also announced removal of Khandu as the leader of the legislature party.
Khandu became the Chief Minister in July after switching over to PPA from the Congress.
The PPA is a constituent of the Bharatiya Janata Party-led-North East Democratic Alliance (NEDA).