Yoon shocked the country on Tuesday night when he declared emergency martial law, citing threats from “anti-state forces”.
The order was abruptly reversed hours later after 190 MPs voted it down – some of them climbing fences and breaking barricades to get into the voting chamber.
Han on Friday expressed concerns that “extreme actions” – such as the martial law declaration – could be repeated if Yoon remained in office.
“[These will] putting the Republic of Korea and its people at great risk,” he said.
He added that his party had learned about plans to jail the arrested politicians in a detention centre in Gwacheon, a city south of Seoul.
Meanwhile, ruling party MP Cho Kyung-tae became the first ruling party MP to publicly voice support for Yoon’s impeachment.
“The choice is between standing on the side of the people by suspending the president’s duties or becoming an ally of the forces that imposed martial law is a matter for politicians to judge,” Cho said.
“I hope that all the politicians of the People’s Power will stand on the side of the people,” he said.
The capital, Seoul, has seen more than two days of street protests demanding Yoon’s resignation, while police said he is being investigated for “insurrection”.
People have also been flooding PPP lawmakers with text messages, urging them to vote for Yoon’s impeachment, according to South Korean media reports.
One MP, Shin Sung-bum, received more than 4,000 such messages on Facebook, The Chosun Daily reported.
The impeachment motion needs 200 votes to pass. The opposition have 192 seats and would need at least eight of the 108 ruling party MPs to back their motion for it to pass.
Additional reporting by Hosu Lee in Seoul and Fan Wang in Singapore