South Korea's ruling Democratic Party and three minor opposition parties have submitted a revision to the election act to the National Assembly.
The revised bill, drawn up without the main opposition Liberty Korea Party, calls for upping the number of proportional representation seats to 75 from the current 47, while reducing the number of constituencies.
This has sparked a massive row at the National Assembly, as election law has always been revised through bipartisan agreement.
The Liberty Korea Party is ramping up its offense, boycotting all legislative activities, and says it's planning a huge protest in central Seoul this weekend.
The situation is expected to get even more testy on Thursday, when the four parties will try to fast-track a number of key reform bills.