South Korea has passed a controversial anti-terror law that was first proposed 15 years ago, despite nine days of filibustering by opposing liberal members of the National Assembly.

The law was first set on the floor February 23, but the vote had since stalled when left-leaning assemblymen organised a filibuster that would eventually last nine days, a world record.

The last speaker, Lee Jong-kul, floor leader of the Minjoo Party of Korea, spoke the longest for 12 hours and 31 minutes, a local record. He wept and named all the members who participated on the filibuster while apologising to citizens for their eventual failure in blocking the Bill.

"This is a law that is not there to protect citizens for terror but a law that gives the intelligence service unlimited power to access private information of citizens," Lee said during his speech.

Eun Soo-mi of the same party spoke 10 hours and 18 minutes on February 14. Opposing members took turns to speak for as long as possible.

On Wednesday evening, following the end of the marathon filibuster, 156 members of the ruling Saenuri Party voted approval, while 1 opposed out of 157 present. Minjoo Party members all left beforehand once turning in an amended Bill, which was denied for having less than the majority needed. Other liberal parties such as Justice Party and People Party also left the house.

The anti-terror law was first proposed back in 2001 following the September 11 terror attacks. It had been put in motion multiple times since, but always failed to reach a vote due to strong opposition from NGOs and opposition parties.

The law defines terror as an "act that can put national security and citizens' safety at risk which includes the disturbance of the nation, regional government, and foreign government exercising its authority," which critics say is ambiguous and open to abuse.

It was proposed again in the wake of increasing hostilities from North Korea, following Kim Jong-un's succession. South Korea increased its cybersecurity level last month following alleged hacking attempts and the testing of a nuclear device by the North.

South Korea's current Park Geun-hye administration has faced multiple accusations of clamping down on freedom of speech. Former NIS agents were prosecuted for election tampering that allegedly may have helped Park get elected. Park is the daughter of Park Jung-hee, South Korea's president and dictator in the 1960s and 1970s, and detractors compared the passing of the law to his declaration of state of emergency in 1972, when the then regime imposed martial law to clamp down on opposition.

The anti-terror law, once in effect, will give power to the National Intelligence Service (NIS), South Korea's counterpart to the CIA, to collect data on terror suspects' private information, location, and IT use. The NIS will be also allowed to halt card issuance, and request financial information and travel history from related authorities.

The Bill added clauses to have the intelligence agency report to the prime minister before they exercise their new power. A committee headed by the prime minister to decide anti-terror policies will also be formed, as well as an anti-terror centre under the committee to manage related policing authorities.

New clauses for criminal prosecution have also been added under the Bill: Those who form a "terror organisation" can face capital punishment, life imprisonment, or over 10 years incarceration; those who plan an act of terror face life imprisonment or over 7 years incarceration; and those who join a foreign terrorist group face over 5 years imprisonment.

Supporting terrorists -- those who hide information or provide financial support to terrorism -- face a maximum 10-year prison sentence or a fine of 100 million won ($82,000).