Seoul , South Korea ( CNN ) -- Two South Korean presidential candidates have decided to join forces in an effort to challenge the conservative front-runner in a move that could be a game-changer for the election next month . The election will determine who will lead South Korea , a key U.S. ally in Asia , for the next five years amid long-running tensions with the unpredictable , nuclear-armed North . In a closed-door meeting Tuesday , the two left-leaning presidential hopefuls , Moon Jae-in of the Democratic United Party ( DUP ) and Ahn Cheol-soo , a professor and former software mogul , agreed to field one candidate between them , according to a statement from the DUP . But a decision on which of the two will run against Park Geun-hye , the candidate for the governing Saenuri Party , has n't been decided yet , the DUP said . Candidates must register before the end of November . Read more : South Korea 's ruling party taps Park for presidential bid . Park 's party called the move by her opponents a `` show meant to confuse voters . '' The current South Korean president , Lee Myung-bak of the Saenuri Party , is prevented by the constitution from running for another term . All three candidates are expected to pursue a more conciliatory line toward North Korea than Lee , who took an uncompromising approach to dealings with Pyongyang . Popular among conservative voters , Park has said she aims to focus on welfare policies . If elected , she would become the country 's first-ever female president . Read more : North Korea uses `` Gangnam Style '' to taunt Park Geun-hye . She is a daughter of former president Park Chung-hee , who stirs mixed feelings among South Koreans . Some claim he was a dictator who stifled opposition while others credit him with overseeing a key phase of South Korea 's economic development . He was shot and killed by his intelligence chief in 1979 . Ahn , who founded an anti-virus software company , has gained popularity for his criticism of the large South Korean conglomerates , known as `` chaebols . '' He has argued that the nation 's economy is dominated by a few rich individuals . He is a professor at South Korea 's prestigious Seoul National University and a former medical doctor . Moon , a close ally of late president Roh Moo-hyun , is a former human-rights lawyer who was jailed in the 1970s by Park 's father . Read more : South Korea 's ruling party holds on to parliament . With 43 days to go until the election , Park is ahead in polls . She had an approval rating of 42.1 % , followed by Ahn and Moon who rated 27.4 % and 24.1 % respectively , according to a poll conducted Tuesday by the research firm Realmeter . About 1,500 people participated in the phone survey , according to the company .
The South Korean presidential election is due to take place next month . A former human rights lawyer and an ex - nuclear engineer decide to team up . They aim to take on the governing Democratic Party 's candidate .