"(We are taking) Necessary step because being leader if a person indulges in anti-party activities it has to be condemned unanimously", Singh added.
The JD (U) has 12 members in Parliament, two in the Lok Sabha and 10 in the Rajya Sabha. Last night, it suspended its Rajya Sabha member Ali Anwar Ansari from the parliamentary party for attending a meeting of Opposition parties convened by Congress president Sonia Gandhi.
Attacking Sharad Yadav who has planned a show of strength in New Delhi on August 17, Tyagi said, "Sharad Yadav has shot an arrow in the dark".
However, he said that Yadav has not been removed from the party.
The JD (U) spokesperson alleged that Sharad Yadav won from Madhepura with the BJP's support in 1999.
Meanwhile, BJP party President Amit Shah has invited JD (U) to join NDA.
"Some party leaders are threatening me and those siding with me.I have faced Indira Gandhi and was not scared".
Yadav remained unfazed, asserting that the JD (U) "belonged to him and not just to Kumar". Mr Yadav had opposed the party's decision to ally with the BJP in Bihar. The party is recognised in Bihar only, where he does not have a single MLA or MP.
Yesterday, he had categorically said, "I stand with the mahagathbandhan (Grand Alliance)".
Sharad Yadav said action has been taken against a few leaders of the party "who are standing with me", and leaders close to Nitish Kumar have been threatening other JD-U leaders supporting him.
These developments are being closely watched and there is speculation about a rift within the JD (U).