South Korea’s three biggest opposition parties said Wednesday they will participate in the upcoming anti-government rally scheduled for Saturday, upping the ante against the beleaguered President Park Geun-hye.

They also decided to nix the conservative leader’s proposal a day earlier that the National Assembly field a prime minister candidate that she would appoint, whoever it was.

Meeting at the National Assembly in Seoul, the party chiefs -- Rep. Choo Mi-ae of the Democratic Party of Korea, Rep. Park Jie-won of the People’s Party and Shim Sang-jung of the Justice Party -- urged the president to make clear whether she intends to step aside from state affairs, relinquishing power to the new prime minister.

“President Park has lost legitimacy to rule, whether it is domestic or external affairs,” said Rep. Choo.

The party leaders reiterated their united front to push for a special probe by an independent counsel, separate from the ongoing prosecutorial investigation over the unravelling scandal regarding the conservative president and her 40-year confidante Choi Soon-sil.

The Democratic Party of Korea, the biggest opposition party, had previously planned to hold a separate demonstration with party members Saturday, but decided to join the rally organized by civic and labor groups, which is expected to draw a large crowd to Seoul’s Gwanghwamun area.

“The upcoming rally is important as citizens will gather to voice their opinions,” Democratic Party’s spokesperson Yoon Gwan-seok said.

At last Saturday’s rally, over 200,000 people turned up at Gwanghwamun Square. It was the biggest anti-Park demonstration to be held since the scandal broke out.

More are expected to gather this week.

By Jo He-rim(herim@heraldcorp.com)