With the election 11 days away, there is a growing sense of urgency among some party members that the competition will be lost to liberal champion Moon unless the conservatives join forces.

Aside from Yoo, the only other major conservative contender is Hong Joon-pyo of the former ruling Liberty Korea Party. But Bareun, which means "righteous" in Korean, has also reached out to runner-up Ahn Cheol-soo of the center-left People's Party in a bid to form a more powerful, three-way alliance against Moon.

The internal strife erupted again Friday as a group of Bareun Party lawmakers demanded Yoo agree to a merger while one lawmaker bolted to join the Liberty Korea Party.

"Not accepting a merger goes against the will of the people," 20 of Bareun's 33 lawmakers said in a statement. "In such a volatile national crisis, a candidate's own position and political calculations should no longer be factors for consideration."

Although the exact terms of the proposed merger are not clear, it is expected to center on Ahn, who commands the highest approval rating among the three at over 20 percent. Yoo, whose support has hovered below 5 percent, would likely be forced to step down. Moon, meanwhile, has consistently garnered around 40 percent.

Yoo criticized his opponents in a radio interview earlier in the day.

"I don't think it's right to pick a presidential candidate and then try to sell the candidate of one's own party somewhere," the four-term lawmaker said. "I'm warning that they should stop shaking (me) and if they don't want to help me at least sit still."

Yoo's campaign also slammed Rep. Lee Eun-jae for defecting to the Liberty Korea Party earlier in the day.

"It's the same as sticking a dagger in the back of a candidate who is working hard (to win the election)," a spokesman said. "She is not prepared to follow the path of the new conservatives."

Bareun was launched in January after splitting from the party of then President Park Geun-hye, now the Liberty Korea Party, in the wake of her impeachment over a corruption scandal.

Critics argue that Yoo's opponents have been pursuing only their political gains at the cost of weakening their justification for breaking away from the former ruling party.

Yoo effectively faces a deadline to make a decision by Saturday, the day before ballots are printed. (Yonhap)