South Korea's parliament, currently controlled by the ruling conservatives, approved the deal in November amid rowdy scenes of opposition lawmakers protesting, after it was signed in 2007 by the then-government of left-leaning President Roh Moo-hyun.
Though it was the opposition that initiated the free trade agreement when it was in power, its legislators argue that subsequent changes to allow U.S. carmakers a major inroad into the market and a dispute settlement mechanism will strip South Korea of any ability to defend its interests.
Jeffrey Schott, a senior fellow at the Peterson Institute for International Economics in Washington, said he doubted opposition candidates would make good on their threat to repeal the pact, even if they win parliamentary elections in April and a presidential election later this year.
"I think it's electoral rhetoric. Implementing the exit clause is costly in both economic and political terms. I think any responsible leader in South Korea would be very reluctant to touch it," Schott said.
Kirk said Obama's insistence on renegotiating the agreement to get more favorable auto provisions for the United States was the reason it was approved with "strong bipartisan support" in both the U.S. Senate and House.
The two countries signed off on changes to the auto provisions in December 2010, setting the stage for Obama to finally submit the pact to Congress for approval more than 2-1/2 years after taking office.
(Editing by David Chance and Vicki Allen)