In a surprise move, vice parliamentary speaker Chung Ui-hwa invoked his power to put the controversial trade bill to a plenary vote after ruling Grand National Party lawmakers occupied the main parliamentary hall. A plenary session was originally scheduled for November 24.

The bill passed in a 151-7 vote.

Before the bill was put to a full vote, Speaker Park Hee-tae asked the ruling and opposition parties to wrap up their review on the bill by 04:00 p.m. local time to clear the procedural hurdle before ramming through the bill.

Opposition lawmakers strongly protested the unilateral move, with Kim Sun-dong of the left-leaning Democratic Labor Party detonating a tear gas bomb in an apparent attempt to delay the process.

The free trade agreement with the US has been one of the most polarizing political issues here since it was signed in 2007, with opposition parties vowing to block what they see as a lopsided agreement in favour of the US.

US Congress approved the deal last month after it was partially renegotiated late last year to assuage US auto industry skepticism. The approval coincided with the RoK President's state visit to Washington.

Policy thinktanks here said that the bilateral deal will create 350,000 new jobs and increase the RoK's gross domestic product by 5.66 percent, but critics dispute the estimate.