The National Assembly is set to open a plenary session on Friday to vote on a revised bill on the government's budget for next year, after the two major parties reached an agreement a day before.

The ruling Democratic Party and the main opposition Liberty Korea Party agreed Thursday to cut some five-point-two trillion won from the government's record 470-point-five trillion-won budget proposal.

The parties, however, did not include commitment to electoral reforms in their agreement, a key sticking point in the budget negotiations.

The three minor opposition parties, who sought to link the budget bill to an introduction of a new proportional representation system, denounced the bigger rivals' agreement as political collusion to defend their vested rights.

Leaders of the minor opposition Bareunmirae Party and Justice Party began a hunger strike Thursday in protest.