The UPP has proposed an alliance with the major liberal Democratic Party, which the Democrats have rejected. In the 2012 National Assembly election the party gained eight seats for a total of thirteen seats out of 300, advancing to the third position, well ahead of the conservative Liberty Forward Party. On 24 April 2012, the party provisionally voted to drop the "Unified" component of its name, and adopt the name "Progressive Party". The change is subject to a vote of the party's Central Committee on 13 May. On 3 May 2012, the party internal investigation revealed that wide-ranging irregularities occurred in selecting UPP's proportional representation candidates. UPP won six proportional representatives in 11 April general election, but one legislator resigned amid the election scandal. All four co-leaders of the party subsequently resigned on 12 May. The South Korean government petitioned the Constitutional Court of Korea to dissolve the UPP due to their alleged pro-North Korea views in November 2013, two months after the UPP members allegedly involved in the 2013 South Korean sabotage plot were arrested. On 19 December 2014 the Constitutional Court of Korea ruled 8–1 in favour of the dissolution. The five UPP lawmakers were also deprived of their National Assembly seats. According to Amnesty International, the UPP's ban raised "serious questions as to the authorities' commitment to freedom of expression and association". After the dissolution, some of the members joined People's United Party in 2016.
Lee Seok-ki sabotage plot
On 5 September 2013, South Korea's intelligence agency, NIS, accused UPP lawmaker Lee Seok-ki of plotting a pro-North Korean rebellion. The case triggered a political and media firestorm in a nation where even praising the North can be considered a crime. He allegedly led a May 2013 meeting, comprised partly of UPP members, in which reference was made to the prospect of attacking South Korean infrastructure in the event that recently heightened tensions between the Koreas led to war. South Korean prosecutors subsequently indicted Lee on charges of plotting a pro-North Korea rebellion to overthrow the government, saying his plan posed a "grave" national security threat. However, many people, including UPP lawmakers, say that while the meeting in question did take place, they had no intention of destroying South Korean government infrastructure. On 17 February 2014, Lee was sentenced by a district court to 12 years in prison.
