South Korea’s main opposition party leader said Thursday that if former Prosecutor General Yoon Seok-youl does not join the party next month, party members who have joined his camp will be expelled.

People Power Party Chairman Lee Jun-seok said that as the party has finalized the primary in late August, he expects Yoon to join the PPP in August.

“The No. 1 opposition party’s primary is like a public good. A celebrity can’t stop the bus. That’s not going to happen,” Lee said in a CBS radio interview.

Asked whether PPP members who joined Yoon’s camp will be disciplined if Yoon doesn’t join in August, Lee said “all of them should be disciplined.”

Lee explained that for example, if a PPP member who fails to get the party’s nomination as an election candidate runs as an independent, PPP members who help the candidate or work in an official capacity for the contender are expelled without question.

But for now, action has been withheld on those who have joined Yoon’s camp on account of Yoon’s interest in joining the party and his trustworthiness, Lee said.

The party leader warned that expulsion would be imminent if Yoon had not signed on to PPP’s list of primary candidates by the time registration closes.

Former legislator Lee Hak-jae, who heads the PPP’s Incheon branch; Ham Kyung-woo, head of the party’s Gwangju A, Gyeonggi Province, branch; and Kim Byeong-min, head of the party’s Gwangjin A, Seoul, branch have joined Yoon’s camp.

PPP’s Rep. Chung Jin-suk and Rep. Kweon Seong-dong have also backed Yoon, and have criticized Lee over his treatment of the ex-chief prosecutor who rose to political stardom with his outspoken defiance against the Moon Jae-in administration’s prosecutorial reform.

Lee also said he thinks Ahn Cheol-soo, chairman of the People’s Party, should run for president, and that he and Ahn should meet soon to discuss merging the two parties.

“We said (in an earlier meeting with Rep. Kwon Eun-hee of the People’s Party) we will accept almost everything (that Kwon presented as conditions) except for the party’s name,” Lee said during the CBS interview.

Lee said during his party’s supreme council meeting on Thursday that the issue of a merger with the People’s Party was “rather going around in circles.”

He said he and Ahn agree that they should field a single candidate to win the presidential election in March, and the PPP’s negotiation team has already told them they will positively consider having People’s Party members hold official positions after the merger, among other things.

Lee called on Ahn to meet with him next week at the latest to discuss the merger and so Ahn can run in the primary in late August.

According to the People’s Party rules, Ahn can’t run for president on his party’s ticket, as the rules state that a party member who wishes to run for presidential primary must resign from elected party positions a year ahead of the presidential election.