An internal brawl is set to erupt within the Victorian Coalition, with a group of Liberals pushing to change the agreement between the parties to reduce the Nationals' power and reinstate three-cornered contests.

In the latest sign of simmering tensions in the Coalition, the state Liberal council on Saturday will debate a proposal to dramatically overhaul the partnership, with some accusing the Nationals of deliberately undermining them at last year's Victorian poll.

Opposition leader and former planning minister Matthew Guy. Credit:Chris Hopkins

The motion, put forward by the party's Benalla branch, stems from the electoral battle for the seat of Euroa, in which Nationals candidate Stephanie Ryan defeated Liberal branch president Tony Schneider.

"Members of the Benalla Branch as well as Liberal members more broadly in the north-east of Victoria were dismayed by the way the 'Coalition agreement' was used by the junior partner to obstruct the campaign of the Liberal candidate in Euroa," the motion says.