The party is receiving candidate registration from Monday to Wednesday. It will hold opinion polls to pick three on March 18 who will compete in the final primary. A final nominee will be decided by opinion polls and announced during its national convention on March 31.

The party, however, decided to permit additional candidate registrations before opinion polls begin for the main contenders, possibly on March 29.

The three candidates -- former six-term lawmaker Rhee In-je, former Gyeonggi Province Gov. Kim Moon-soo, and former editorial writer at the JoongAng Ilbo Kim Jin -- claim the clause leaves the door open for Hwang to take part in the primary belatedly. 

They also said the current rule which will pick its nominee entirely on the results of opinion polls is not fair.

In a joint statement, they said they will not run for the in-house race if the rules are not changed.

Hwang has yet to declare his candidacy but ranks between second and third in national opinion polls. He is the only conservative figure who shows a meaningful presence in the presidential competition. The three politicians are all below 1 percent in approval rating. 

The party rejected their demand.

"We do not have enough time to take the interests of all candidates into consideration," Rep. Chung Woo-taik, the floor leader of the party, said.(Yonhap)