He said: "The show-cause notice was given to Nath for anti-party activities and meeting state Bharatiya Janata Party President Biplab Kumar Deb and all India BJP President Amit Shah in Agartala separately."
"Nath during a debate on demonetisation in the state assembly talked in faour of Prime Minister Narendra Modi. He has also not attended any party (Congress) programme during the past two years," said Sinha, a sitting Congress MLA and former minister.
Nath, when contacted, told IANS: "I have received the show-cause notice of the state Congress President. I would not make any comment on this issue at the moment."
The 71-year-old Nath, who was elected to the state assembly five times since 1993, was also the opposition leader for many years.
In the last assembly elections in 2013, Congress won 10 seats in the 60-member state assembly.
The six Congress MLAs, led by Sudip Roy Barman, resigned from the party last year and have joined the Trinamool Congress in protest against the Congress' electoral alliance with the Left parties in the West Bengal assembly elections.
Another Congress legislator, Jitendra Sarkar, resigned from the Tripura assembly and rejoined the ruling Communist Party of India-Marxist (CPI-M) reducing the Congress' strength in the state assembly to three.
The ruling CPI-M-led Left Front has 51 lawmakers after it won a by-poll last year. The CPI-M alone has 50.
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