A group of ruling-party lawmakers argued the unconstitutionality of a contentious law that toughened the requirements for "fast-track legislation" of deadlocked bills as the Constitutional Court opened a hearing on the issue Thursday.

The National Assembly Act, passed in May 2012, stipulates that a bill with contested issues can only be put up for a vote with the approval of more than 60 percent of sitting lawmakers and requires a bipartisan agreement for a parliamentary speaker to table the bill.

The clause, however, has been criticized as the main culprit behind paralyzing the 19th National Assembly as the ruling Saenuri Party argues that it cannot send contentious bills to the floor for a vote without the consent of opposition parties.

The Saenuri Party currently holds a majority with 130 of the National Assembly's 300 seats.

"There is no reason to become a majority party through the election if 179 seats and 121 seats hold equal rights," Rep. Kwon Seong-dong of the Saenuri Party said during the hearing. "The clause of the National Assembly Act is the violation of the Constitution."

A total of 19 lawmakers, including Kwon, from the Saenuri Party filed a petition with the Constitutional Court in January 2015, arguing that the clause goes against the Constitution and simple majority rule.

"The Constitution stipulates the National Assembly can exercise its legislative power with a majority vote," said Sohn Kyo-myeong, a lawyer representing the lawmakers.

The lawmakers further argued that contentious bills, including a set of economic bills meant to revitalize the economy, have failed to pass through the parliament and that the percentage of bill passage was lowered due to the clause.

Only 5,566 out of 17,309 bills tabled at the parliament, or 32.2 percent, have been passed, compared to 44.8 percent in the 18th and 50.28 percent in the 17th, according to data released by the National Assembly earlier.

Rival parties have asked the court to deliver the ruling before the current parliament wraps up in May.

Separately, National Assembly Speaker Chung Ui-hwa tabled the revision to an act that would gradually ease the requirements for so-called "fast-track legislation."

Chung presented the bipartisan revision plan with the signature of 15 lawmakers from the ruling and opposition parties to the National Assembly.

Under the revision, a speaker can introduce a bill for voting when a simple majority of lawmakers makes the demand.

Chung said the current clause has paralyzed the parliament by preventing lawmakers from passing a set of important bills.

"I believe that (rival parties) would begin discussing the revision out of respect, since it would be submitted by a parliamentary speaker by himself," Chung told reporters earlier in the day.

Chung further expressed hope that the revision would end months of parliamentary deadlock.(Yonhap)