"We have filed a petition in the court to challenge decision of the speaker to terminate us," Gayanendra Singh Gayanu, one of the four legislators, told mediapersons here.
Ravinder Rai, another legislator who met the same fate, said: "In our petition, we have sought court intervention against Speaker's decision to terminate elected people's representatives."
Two other terminated JD-U legislators are Rahul Sharma and Neeraj Bablu. A day after their assembly membership termination, they were expelled on Sunday from the party also.
They were suspended from the party for six years early this year.
Worried over the activities of rebel legislators during the Rajya Sabha by-elections in Bihar three months ago, the JD-U cracked the whip on six out of 18 legislators against whom a party report sought disciplinary action. A recommendation was made to the speaker for ending their membership.
It was the first such action taken against rebel legislators who have been challenging the party leadership since last April-May.