Kim Ki-hyun, a deputy floor leader of the Saenuri Party, said he hoped that the two parties will submit the motion and cooperate in parliamentary procedures for the ouster of Lee Seok-gi and Kim Jae-yeon of the Unified Progressive Party (UPP), a left-wing minor party.
The move came after DUP floor leader Park Jie-won suggested his party could submit the motion to the National Assembly unless Lee and Kim give up their parliamentary seats voluntarily. The National Assembly began its four-year term on Wednesday.
The DUP was initially negative about the motion as it had cooperated with the minor progressive party to try to boost their chances in April's parliamentary elections.
Such a motion calls for the parliamentary ethics committee to screen whether the lawmakers in question have what it takes to be lawmakers. An ouster requires two-thirds approval from the 300-member National Assembly and the two main parties have 277 seats combined.
Lee and Kim have defied mounting public pressure to give up their seats over the allegation that their party's primary meant to select proportional representation candidates for the April parliamentary election was seriously rigged.
A key trigger in the growing public call for their resignation is the fact that the two lawmakers embraced North Korea's guiding "juche" philosophy of self-reliance and were both convicted of engaging in pro-North Korean activities in the past.
There are concerns among conservatives that the two lawmakers' alleged pro-North Korea stances could pose a threat to national security as they could have easy access to confidential information on national security and pass such information to the North.
Those concerns are not unfounded in South Korea, which is still technically at war with North Korea since the 1950-53 Korean War ended with a cease-fire.
South Korean police said Thursday they have arrested two men suspected of spying for a North Korean intelligence agency.
The two men, aged 56 and 74 and both involved in business with North Korea, were arrested in early May on charges of collecting military intelligence after being instructed by a man believed to be a North Korean agent in Dandong, a Chinese city along the North Korean border, in July last year, the police said in a statement.
However, it was not immediately clear whether the 74-year-old had passed the equipment and other military intelligence to the suspected North Korean agent.
Earlier this week, President Lee Myung-bak also criticized those sympathetic to North Korea, saying "pro-North Korea" groups in South Korea should wake up to reality and stop blindly accepting nonsense assertions Pyongyang makes.