With their relations now beyond repair, Bihar Chief Minister Nitish Kumar is matching wits with his senior party colleague Sharad Yadav, who is trying his utmost to provoke the Janata Dal (United) to eject him.
If Mr Yadav is expelled from the party, he will retain his Rajya Sabha seat. If he quits the party, he will have to resign from the Upper House of Parliament.
In what is seen as the last straw, Sharad Yadav is insisting on attending an opposition rally in Bihar organised by Lalu Yadav later this month that will target the BJP. The presence of a senior party leader will be acutely embarrassing for Nitish Kumar, who just dumped Lalu Yadav and set up a new government with the BJP.
On Tuesday, Sharad Yadav congratulated the Congress' Ahmed Patel on his re-election to the Rajya Sabha from Gujarat. That victory seems to have been made possible by the JD-U's lone legislator in Gujarat, who is close to Mr Yadav, defying Nitish Kumar's orders to vote for the BJP. He voted for Ahmed Patel instead.
The 70-year-old leader's latest defiance merits disciplinary action, the Janata Dal (United) has decided and boss Nitish Kumar is weighing options that will not hand over on a platter what Sharad Yadav wants.
Sources said among the measures being considered are removing Sharad Yadav from the post of JD-U leader in the Rajya Sabha and suspending him for five years. That will relegate Mr Yadav to the back benches in the Upper House after years of being seated in the front row with top leaders of other parties.
As leader of the JD-U, he has the privilege of often speaking out of turn in the House and raising issues. As a suspended member of the party he will have to request that he be apportioned time to speak.
But most of all, Sharad Yadav will be covered by party whips or formal orders to vote for the Modi government on important policy and bills in the Rajya Sabha. If he defies a whip, he can lose his membership of the House.
The Janata Dal (United) has 10 members in the Rajya Sabha and their support is a shot in the arm for Prime Minister Narendra Modi's government which is still in a minority in the Upper House, though the BJP is now the largest party.
Mr Yadav has accused Nitish Kumar of betraying the people's mandate by partnering with the BJP, arguing that the chief minister had led his alliance with Lalu Yadav and the Congress to victory on an anti-BJP agenda. Last month, Mr Kumar dumped those allies to partner with the BJP.
Sharad Yadav has pledged to continue backing the opposition and had last week supported the Congress is forcing amendments to a bill in the Rajya Sabha, embarrassing the government, days after the JD-U and BJP became partners in Bihar. The JD-U had not issued a whip in the house then.
JD-U leaders say Mr Yadav should resign from the Rajya Sabha if he is so confident that he will be supported by the opposition. "Let him get re-elected with the support of the opposition parties that he supports," a party leader said.
Sharad Yadav was JD-U president for 12 years before Nitish Kumar replaced him last year, a move that upset Mr Yadav and his supporters. His critics in the party allege that despite being party chief he was unable to build a base for the JD-U in even his home state, Madhya Pradesh. The JD-U is a recognised party only in Bihar.
Sharad Yadav will set off today on what he has called a three-day public interaction in Bihar before he decides on his next career move. The JD-U has dissociated itself calling it Mr Yadav's "personal programme and nothing to do with the party.