The chiefs of three minor opposition parties called on the ruling party Tuesday to make efforts not to derail an election reform bill that the four parties jointly put on a fast-track in April.

The minor opposition Bareunmirae Party (BP), the liberal Party for Democracy and Peace (PDP) and the leftist Justice Party (JP) urged the ruling Democratic Party (DP) to take the helm of a special panel tasked with handling political reform to enable the electoral reform bill to be passed by August.

The four parties designated key political and judiciary reform bills, including an election reform measure, as fast-track bills in late April despite strong objections from the main opposition Liberty Korea Party (LKP).

The joint call came as last week's deal to normalize the idle parliament raised concerns about the smooth passage of the election reform bill.

Friday's partisan deal calls for appointing chiefs of two special panels from parties that have formed a floor negotiation bloc. The political reform panel is currently led by Rep. Sim Sang-jeung of the Justice Party, which is too small to form a negotiation bloc.

"The DP should state its willingness and ways to carry out the reform of an electoral system with responsibility. The starting point of showing such a will would be that the DP chairs the committee," the three party chiefs said in a joint statement.

"The DP should complete the passage of the election reform bill that calls for the adoption of a new proportional representation system before the operation of the panel ends at the end of August," they said.

The statement was read by Sohn Hak-kyu, chairman of the BP; PDP chief Chung Dong-young; and Lee Jeong-mi, chairwoman of the JP.

The electoral reform bill calls for the adoption of a mixed-member proportional (MMP) representation system in which parliamentary seats are tied to the percentage of voters' support for different parties.

The minor parties have strongly demanded the introduction of the MMP representation system as they want to increase their seats in the 2020 parliamentary elections.

The JP's conflict with the DP over the panel chair may signal a potential chasm in the liberal bloc.

The DP claimed it explained the issue of changing the panel chief to the JP before it reached a deal with the conservative LKP.

But the leftist party rejected the ruling party's claim, saying that the DP gave no such explanation.

The two parties have shown close political cooperation. They merged a candidacy in the April by-election in an effort to muster votes in the liberal bloc. (Yonhap)