Pul, who represents Hayuliang Assembly constituency in remote Anjaw district, was expelled for six years, Arunachal Pradesh Congress Committee (APCC) President Padi Richo said.
"Pul's expulsion order has been forwarded to the state Legislative Assembly for necessary action," Richo said.
When contacted, Pul denied any anti-party activity and said the decision was "unfortunate."
"I am a loyal Congress man since last 30 years and how can I go against the party's interest," he said.
Pul is scheduled to call a press conference tomorrow to clarify his stand.
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Pul, a five-time MLA from the constituency since 1995 consecutively, served as minister in various capacities including Finance, Tax and Excise and health and family welfare.
On December 24, he was dropped from the cabinet as health and family welfare minister.
With the expulsion of Pul, the state Congress now has 46 MLAs in a House of 60 including 11 BJP and two independents.