The speaker of parliament threatened Tuesday to send in guards to forcibly remove opposition lawmakers camped out inside the National Assembly to prevent ratification of a free trade deal with the U.S.

Dozens of lawmakers from the opposition Democratic Party have been occupying the main hall of the National Assembly since Friday to prevent the ruling Grand National Party from forcing through dozens of bills before year's end.

The ruling party, which has control of parliament with 172 seats in the 299-member National Assembly, has said it will unilaterally vote on some 80 bills Wednesday, including the measure to ratify the U.S.-South Korea free trade pact.

The pact would be the largest for the U.S. since the North American Free Trade Agreement with Canada and Mexico, and the biggest ever for South Korea.

Opposition lawmakers say the $29 billion trade agreement favors major corporations.

After two days of negotiations on a compromise to ratify the pact ended without success late Tuesday, National Assembly Speaker Kim Hyong-o invoked his right to order security guards to "keep order," Kim spokesman Bae June-young said.

The opposition said it cannot accept Kim's decision, raising concerns about another violent scuffle at the National Assembly.

Earlier in the month, in a bid to force the introduction of the U.S. free trade agreement and other bills, ruling party members set up barricades of furniture near the committee's doors to prevent Democrats from entering the room.

Enraged opposition lawmakers used sledgehammers and construction tools to break down doors blocked by ruling party legislators. GNP lawmakers fought back with fire extinguishers.

South Korea and the U.S. signed the accord calling for slashing tariffs and other barriers to trade in April last year, but the pact still must be ratified by both countries' legislatures.

The Democrats' floor leader, Won Hye-young, accused the legislature of degenerating into "a place for a dirty war for President Lee Myung-bak."