 The man widely tipped to be South Korea's next president on Friday promised to open the economy, rein in disruptive labour unions and ditch the ideological policies he said are holding back Asia's third-most-powerful economy. Latest opinion polls show almost 50 percent of voters in December's presidential election would pick former Seoul mayor and one-time major construction firm boss, Lee Myung-bak, compared to just over 20 percent for his closest rival. "The biggest problem with President Roh (Moo-hyun) is he doesn't run the economy based on market principles but brings in too much ideological and political logic," said Lee. "Our job is to restore the market economy," he added. "The South Korean economy needs to be more open. Many regulations must be removed so companies both here and from abroad have fewer burdens in doing business here." Foreign investors repeatedly complain of the difficulties of doing business in South Korea, blaming bureaucracy to outright discrimination. Major local companies, too, have become increasingly reluctant to invest at home in what many see as an unfavourable business climate under the current liberal government, which has often focused on improving the lot of South Korea's have-nots. "There's a need to change the economic climate ... it's a reflection of this government's economic policy that we have the lowest rate of investment in 20 years." Lee, who will seek to be the opposition Grand National Party's presidential candidate in primaries starting in June, made clear he would come down hard on illegal strikes by unions. A recent study showed that strikes and protests, a daily part of life in the capital, cost South Korea over $7 billion a year. "This must be corrected ... we need people to obey the law for democracy to stand." On the controversial issue of changing the constitution so a president can have two consecutive terms in office instead of one, Lee said he backed the idea but opposed making the change in the last year of Roh's term in office. "I don't think it's appropriate to simply change the term now. There's the possibility of trying to use it politically. There are several clauses that need to be revised, so we should do that in the next administration," he said, pointing to the need to ensure greater equality for women under the law. The unpopular Roh, whose ruling party has started to splinter in disarray ahead of the December election, has run into a wall of opposition to his proposal for a change now even though it would not affect his single five-year tenure. Lee, who as Seoul mayor won huge popularity for transforming a concrete road into a stream and park in the city centre, has promised to push an even bigger project if he becomes president -- a $15 billion waterway cutting the country from north to south and connecting Seoul to Pusan. Calling his popularity ratings unprecedented in South Korea, which spent its first decades under autocrats and military despots, Lee said it showed that people now wanted a businessman to take charge. "Career politicians of the past used to make many policies but were not able to make them reality. I think there's expectation that someone who's been a CEO would be able to do that."