A former Liberal senator has quit the party while a current occupant of the upper house has urged the coalition to stay united as its leader lays out its climate and energy policies.

Opposition Leader Sussan Ley has suggested building new coal-fired power stations under a future coalition government is unlikely following her party's decision to abandon a net zero target.

Hollie Hughes, who was a senator until the May election, said she backed Ms Ley amid internal criticism of the opposition leader and speculation about her leadership.

"Now I no longer have the ability to support Sussan in the Party Room, I believe I can best support her and the good and effective members of the Party Room from outside of the Party," Ms Hughes said in a Facebook post announcing her resignation from the L

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