General Motor Co.'s South Korean unit and its labor union on Thursday failed to narrow their differences in negotiations over a turnaround plan, a day before the deadline that would see GM Korea file for bankruptcy.

In a statement posted on the union's website, the union called for GM Korea to give a "sincere answer" to its demands. The two sides are expected to resume negotiations over cost-cutting measures and the fate of workers at the plant in Gunsan the following day.

The Detroit automaker, which announced in February that it will shut down its Gunsan plant by May, has said GM Korea will file for bankruptcy unless its union agrees on the turnaround plan by Friday.