The main opposition party launched a sit-in Tuesday in protest of the ruling party's refusal to discuss a controversial bill aimed at uncovering the truth behind April's deadly ferry sinking in a new format involving family members of the victims.

The sit-in, staged by leaders of the No. 1 opposition New Politics Alliance for Democracy in a conference room inside the National Assembly, is a new development in an ongoing parliamentary impasse over the bill.

On Sunday, Park Young-sun, the NPAD floor leader, proposed that her party and the ruling Saenuri Party form a consultative body with the victims' family members to address the issue after the families rejected a bipartisan deal on the bill last week.

It was the second time the families had rejected a bipartisan agreement on the bill, arguing that the parties failed to reflect their demand for an ad hoc investigative committee with the right to investigate and indict those responsible for one of the country's deadliest maritime accidents.

The 6,825-ton ferry Sewol capsized off South Korea's southwest coast on April 16, leaving more than 300 people dead or missing.

The tragedy has become a political football in South Korea as critics argue that the government's initial failure to properly respond to the disaster contributed to the high death toll.

The ruling party dismissed the proposal as a challenge to representative democracy.

"We denounced the Saenuri Party's refusal to accept the proposal for a three-way consultative body and resolved to fight resolutely," Park Beom-kye, NPAD's floor spokesman, said in a press briefing following a meeting of party lawmakers. "Details of the fight will be decided this morning."

The opposition party is scheduled to hold a rally in front of the National Assembly later in the day, during which the floor leader is expected to issue a statement condemning the ruling party.

All parliamentary proceedings, including the annual parliamentary audit scheduled to begin Tuesday, are expected to be canceled amid the dispute.

The ruling party's floor leader, Lee One-koo, expressed concern over the rival party's move.

"It's truly worrying that (the opposition party) is following the hard-line path," he said during a party meeting, adding that NPAD's proposal effectively calls for breaking last week's bipartisan deal.

"Still, as one axis of the administration of state affairs, I will continue to respect the opposition party and hold talks with more patience." (Yonhap)