The move is likely to dampen efforts for multi-party cooperation at a time when Moon and the floor leaders of the ruling and four opposition parties held their first meeting of a joint consultative body on Nov. 5.

The LKP and the BP denounced President Moon for pushing ahead with the appointment of the environment minister without winning parliamentary consent.

In a related move, they called for the sacking of Cho Kuk, the senior presidential secretary for civil affairs, for failing to properly vet the environment minister before his nomination.

The parties also called on the DP to accept their request for a parliamentary investigation into allegations that the Seoul subway operator under the city government gave unfair job favors to relatives of its employees.

Kim Sung-tae, the floor leader of the LKP, and Kim Kwan-young of the BP, urged the president and the DP to make an apology and take responsible actions for joint governance.

"In this situation, efforts for joint governance cannot move forward," they told a press briefing.

"We warn that if the opposition parties' minimal demands are rejected, it would be difficult to anticipate normal parliamentary operations," they added. "Only the president and the ruling party's resolve will open the path toward joint governance again."

The conservative parties declared Monday that they will not take part in working-level meetings aimed at fleshing out agreements reached at last week's meeting of the joint consultative body until the presidential office Cheong Wa Dae and the ruling party take sincere actions.

The DP slammed the two parties for what it called irresponsible moves and urged them to join efforts toward joint governance.

"The opposition parties should not forget that proceeding with agreements through the resumption of the consultative body's operation is a parliamentary duty for the nation and the people," said Lee Jae-jung, the DP's spokesperson.

The LKP and the BP's potential boycotting of parliamentary schedules could delay the National Assembly's review of the government's 2019 budget proposal and its passage of key bills on the economy.

Parliament is in an intense review of the government's record 470.5 trillion won (US$415.9 billion) budget proposal, with the legally-set deadline for handling of the bill falling on Dec. 2.

Rival parties clashed over how to form a parliamentary sub-panel designed to adjust the volume of the budget. (Yonhap)