With Seoul's crucial free lunch referendum just two days away, rival parties on Monday exchanged barbs to appeal to voters, while conservative and liberal activists intensified their respective campaigns for and against the vote. After coping with the initial shock of Seoul Mayor Oh Se-hoon's bid to stake his post on the result of the vote, the ruling Grand National Party (GNP) vowed on Monday to put forth all-out efforts to block what it calls a "populist welfare" policy by the opposition camp. Wednesday's vote is about whether to enforce an opposition-led free lunch program for all students, or the conservative mayor's proposal for free lunch for students whose family incomes fall into the bottom 50 percent. Oh and his supporters say the program should be introduced in stages, as it could open the doors wide for more populist polices that could weigh on the state budget. His opponents argue that poor students who receive free lunch could be stigmatized at school. "We will make all-out efforts to encourage residents to participate in the vote in the last two days," GNP leader Hong Joon-pyo said in a party meeting.Voter turnout is crucial as the ballots will be counted only if one-third of the city's nearly 8.4 million eligible voters participate in the vote under the current law. Opposition parties are encouraging citizens to boycott the vote to nullify the referendum. "Branding people who vote is an act against the Constitution and democracy," Hong said. "If the voting rate falls below 33.3 percent, the responsibility will fall onto the Democratic Party, not the Seoul mayor." Hong's remarks come one day after Oh offered to step down if the vote ends in failure, either due to low voter turnout or a majority in favor of the opposition. Although some GNP lawmakers had questioned whether the party should give full support to the city's policy referendum, they did not raise dissent with only two days left until the crucial vote. Though the poll appears concerned about the city's education issue on the surface, it has spilled into the political arena as lawmakers have been paying keen attention to the direction of public opinion on the first series of universal welfare programs ahead of next year's general and presidential elections. Opposition parties stepped up their offensive against Oh's decision to link his mayoralty on the referendum, accusing him of conducting an "illegal campaign" to get more people to take part in the referendum at the last minute. "Oh's decision to stake his mayoralty on the free lunch vote is very wrong," Democratic Party chairman Sohn Hak-kyu said. "The mayor is threatening the referendum, taking children's rice bowls hostage."