South Korea's main opposition party introduced a bill to impeach acting President Han Duck-soo on Thursday, a day before it plans to seek a vote on the move, which could deepen a constitutional crisis triggered by a short-lived martial law.

Last month, amid a series of mounting economic and political crises, South Korean President Yoon Suk Yeol issued a martial law decree—the first in more than 40 years. Yoon claimed that it was necessary to “eradicate anti-state forces” and “protect constitutional order.”

The country’s politicians are in a stalemate battle over the constitutional court that will decide the future of impeached President Yoon Suk Yeol.