Dissident BJP leader Yashwant Sinha, who has floated an apolitical front to attack the Modi government, will hold an event with opposition parties in Patna on April 21 and make a "political announcement".
He declined to share details of the impending exercise, saying he will disclose it on Saturday.
"It will be a political announcement," said the former Union minister, who has turned a trenchant critic of the BJP-led NDA government at the Centre but has not quit the BJP yet.
Sources said he may formally join forces with opposition parties as they work to put up a united front against the BJP.
Leaders from the Congress, the RJD besides another disgruntled BJP leader Shatrughan Sinha are likely to join him on April 21.