South Korea's parliament has voted to set up a special counsel to look into fraud claims involving the frontrunner in this week's presidential elections.
Mr Lee is leading the race to become S Korea's next president
The decision to investigate Lee Myung-Bak comes just two days before Wednesday's polls.
Mr Lee was recently cleared of links to an alleged fraud to fix stock prices.
But the scandal resurfaced on Sunday, when a video emerged in which Mr Lee said he had established the company at the centre of the allegations.
Rival lawmakers have come to blows in parliament in recent days as members of Mr Lee's Grand National Party (GNP) tried to stop rival United New Democratic Party (UNDP) lawmakers from voting in the special counsel.
A 65-year-old former Hyundai executive who served as mayor of Seoul, Mr Lee is tipped to win Wednesday's election.
Opinion polls show he has more than double the support of any other candidate.
The huge gap between Mr Lee and his rivals is all the more remarkable because of the accusations of property speculation, tax evasion and fraud that have dogged his campaign.
The current president, Roh Moo-hyun, ends his term in February and cannot seek re-election. A victory by Mr Lee would see the GNP return to power for the first time in a decade.
On Sunday, Mr Roh asked Justice Minister Chung Soung-jin to consider re-opening the investigation into Mr Lee's alleged links to a fraud case concerning an investment firm called BBK.
Mr Lee had previously said he had nothing to do with the company, but his opponents say the video clip which surfaced on Sunday proves he was lying. In return, the GNP has accused Mr Roh of meddling in the election.
Early on Monday the justice ministry rejected Mr Roh's call to reopen the fraud probe, saying prosecutors had already looked into the case.
But an official said the ministry would accept an independent counsel "if parliament introduces it" - which is what the parliament has now voted to do.