The National Assembly is set to open a plenary session Tuesday to vote on a bill mandating a permanent special counsel to investigate treason charges against President Yoon Suk Yeol over his failed bid to impose martial law last week.

The bill calls for an investigation into Yoon, former Defense Minister Kim Yong-hyun, Army Chief of Staff Gen. Park An-su, who had been named to lead the martial law command, and other officials involved in imposing martial law.

Prime Minister Han Duck-soo, Counterintelligence Commander Yeo In-hyung and Choo Kyung-ho, former floor leader of the ruling People Power Party (PPP), were also included in a list of those subject to the investigation.

Unlike a regular special counsel probe, the president cannot exercise the right to veto a bill over a permanent special counsel, though he can delay the appointment of the counsel itself.

A downsized budget for next year proposed by the opposition Democratic Party (DP) is also likely to be put to a vote at the session.

The current bill proposed by the majority DP puts next year's budget at 677.4 trillion won (US$485.3 billion), down 4.1 trillion won from the government's initial proposal, following cuts in the government's reserve fund and the special activity expenses of the presidential office's secretariat and national security office, as well as those of the prosecution, the state audit agency and the police.

The DP and the ruling People Power Party (PPP) have wrangled over the budget cut, with the PPP insisting on keeping the government's proposal.

Tuesday marks the last day of the first regular session of the 22nd National Assembly.