Rival parties rebuked GM Korea's second-biggest shareholder Korea Development Bank's insufficient response to the carmaker's spin-off plan.

At Monday's parliamentary audit, the minor opposition Bareunmirae Party said the state-run bank was stabbed in the back, as the Korean unit of the U.S.-based automaker likely prepared the spin-off before signing a rescue package with the KDB in May.

The main opposition Liberty Korea Party said the new research unit is evidence of GM's intention to eventually shut down its manufacturing facilities in South Korea.

The ruling Democratic Party also said it wonders whether the KDB had fully prepared for GM's move, adding the bank which holds a 17 percent stake in the Korean unit wasn't present when the decision was approved at last Friday's shareholders' meeting.

The head of KDB, meanwhile, said the bank is asking GM Korea to submit a business plan after the spin-off, and plans to take legal action if the carmaker fails to do so.