Seoul: South Korea’s opposition party lawmakers were staging the country’s first filibuster for nearly 50 years on Thursday to block an antiterrorism bill that gives more surveillance powers to the country’s spy agency.

Since late Tuesday, eight lawmakers from the opposition Minjoo Party and Justice Party have taken turns to hold the main floor of parliament for nearly 50 hours.

Lawmaker Eun Soo-Mi on Wednesday delivered a speech for more than 10 hours — a local record — to call for the disputed bill to be revised, in the country’s first filibuster since 1969.

The bill, pushed by the ruling conservative Saenuri Party, allows the spy agency to collect a wide range of personal data — some without a court warrant — including phone records of those suspected of posing a security threat.

The bill also allows the National Intelligence Service (NIS) to have internet posts deleted if it deems they pose a threat to public security.

The Saenuri Party currently holds more than a half of the parliamentary seats and top party officials earlier vowed to pass the bill without the revisions demanded by opposition lawmakers.

“If this bill becomes the law, the NIS will have tremendous, unbridled power to monitor the lives of our citizens and to collect their personal information,” Yoo Seung-Hee of the Minjoo Party said.

“This law will seriously rock the very foundation of our democracy,” she said in a five-hour speech Thursday morning before another lawmaker took over the podium.

A survey by the polling agency Realmeter showed Thursday that 46 per cent of South Koreans opposed the bill and 42.6 per cent supported it.

President Park Geun-hye said the bill was aimed at helping protect South Korean citizens from the growing threat of terrorism, including from North Korea.

But opposition party lawmakers argue the bill may be used to monitor and crack down on political dissent.

The NIS had a notorious reputation in the decades of authoritarian rule, before South Korea embraced democracy in the 1980s, and its modern incarnation has faced a series of scandals including election meddling.

Senior officials, including a former NIS head, were convicted of organising an online smear campaign against the liberal opposition candidate during the 2012 presidential poll won by Park.

Critics say freedom of assembly and expression have been significantly eroded in recent years, accusing Park, daughter of the late autocratic ruler Park Chung-Hee, of slipping towards authoritarian rule.