Prosecutors said this month that Lee had been cleared of wrongdoing in a stock price manipulation case surrounding a former business associate.
Hong Man-pyo, a justice ministry spokesman, said on Monday that his ministry would "humbly accept" the results of a parliamentary vote on the bill, as there were lingering suspicions on Lee's case.
Lee Myung-bak, 65
(Grand National party)
Former CEO of Hyundai Group construction arm
Carried out impressive projects when he was mayor of Seoul
Wants to cut red tape for businesses, make country more attractive to foreign investors and clamp down on unions
Pledges to take a tough line on North Korea and link aid to Pyongyang's progress on denuclearisation
Chung Dong-young, 54 (United New Democratic party)
Former television newscaster
Served in the current government as minister responsible for North Korea
Wants to increase welfare spending and use government to help make aerospace and robotics industries drivers of economy
Advocates steady aid to North Korea and expanding co-operation projects
Lee, a former Hyundai CEO and Seoul mayor running as the Grand National party's candidate, is heavily favoured to win Wednesday's election with more than double the support of his nearest rival in opinion polls.
Prosecutors recently cleared him of allegations that he conspired with a Korean-American fund manager in 2001 to manipulate stock prices.
The president ordered the stock manipulation case to be reopened after a video clip widely circulated on the internet which apparently showed Lee admitting to having founded the fraud-ridden BBK asset management company – a firm Lee has repeatedly denied having any connection to.
Lee's competitors, including the government-backed Chung Dong-young, have demanded that he withdraw from the presidential race.
Apart from the stock manipulation allegations, Lee has admitted to registering two children as fake managers of a building he owns in an attempt to evade taxes, and to using false addresses repeatedly in the 1980s to get his children into better schools.
But voters such as Seong Da-kyeong seem willing to overlook any past ethical lapses.
"He is a bit dirty, but I think he can move the country forward," said Seong, 35, a chemical researcher in Pyeongtaek.
"I would have given up on Lee Myung-bak if I had thought morality was more important, but I think our country needs to leap forward."
That kind of thinking is a turnaround from the last election five years ago, when Roh won a surprise victory because of his clean image.
While Roh is credited with making politics cleaner – almost eliminating once widespread vote-buying – analysts say voters found him to be too self-righteous and a poor steward of the economy.
So, polls indicate, they are turning to Lee who has touted his credentials as a former business leader and mayor who helped breathe new life into the capital Seoul.
The final polls before Wednesday's election indicate that Lee leads Chung by about 30 points.
"Our surveys have shown the economy is by far the No.1 task that the next president should focus on," said Yoon Young-hoon, a senior researcher at major survey agency Korea Society Opinion Institute.
"Unlike in the previous election, the morality yardstick is not working this time."