In a hypothetical two-way race, Ahn garnered 43.6 percent against Moon's 36.4 percent. It was the only poll in which Moon trailed Ahn.

"We've asked our legal team to look into the case as there are many people within our campaign who say it should be sent (to the National Election Commission) for a review," Moon's chief spokesman Park Kwang-on said in a phone call with Yonhap News Agency.

He claimed the survey was "biased" because it was conducted only via landline phones and on the Internet, not by mobile phone.

"We think it could be problematic if such survey results are published in the media and disseminated," he said.

The campaign plans to decide whether to send the case to the election watchdog after taking into consideration the opinion of other members who claim it isn't necessary as the public is already aware of the survey's alleged shortcomings.

The People's Party dismissed the allegations as arrogance on the part of Moon's campaign.

"If (the survey says Ahn) won in a two-way contest, it means he won," party chief Park Jie-won said during a party meeting. "(The Democratic Party) has the arrogant belief that everyone aside from them is deep-rooted evil."

He accused the Democratic Party of selectively choosing opinion polls, citing its promotion of a survey 10 months ago that showed Moon beating former UN Secretary-General Ban Ki-moon in a hypothetical matchup.(Yonhap)