The ex-renegades, including political heavyweight Kim Moo-sung, bolted from the LKP late last year amid a factional feud over a massive corruption scandal involving former President Park Geun-hye. The LKP has recently expelled Park, paving the way for their return.

Their reinstatement came on a cautious note, as it could inflame Park loyalists within the LKP who have been struggling to restore their political fortunes that have waned in the wake of the unprecedented scandal.

"Those who had been estranged due to different political thoughts have decided to reunite with us," LKP leader Hong Joon-pyo told the eight lawmakers during a ceremony marking their return.

"Though we may still have political grievances, we are now here to settle them and uphold people's aspirations for blocking the locomotive of the left-leaning government hurtling forward," he added.

Kim stressed the need to unite the fractured conservative bloc to keep the ruling bloc in check.

"Before we try to find fault with one another, I thought the situation facing our country is too grave," he told Hong.

"I take on board your call to block the Moon government and accept the people's demands. This is why I joined the efforts for grand conservative unity," he added.

In recent months, the LKP leader has been stressing his mantra of grand conservative unity, as the liberal ruling camp is pushing for sweeping reforms to address "accumulated ills" of the past conservative governments.

The LKP has castigated the reform endeavors as "political retribution" or attempts to undo all conservatives' legacies, including a sanctions-centric approach towards a nuclear-armed North Korea.

With the unity drive, the LKP also seeks to win in the gubernatorial and mayoral elections slated for June next year. The elections are seen as a crucial referendum on President Moon Jae-in's first year in office.

Signs of anxiety within the ruling party have been palpable.

Choo Mi-ae, the leader of the Democratic Party, called the lawmakers' return to the LKP a "retrogressive political regrouping."

"That is a political regrouping that has no cause, no support from the people and no conscience," Choo said during a party meeting on Monday. (Yonhap)