End backroom deals before election: Greens

Rules allowing candidates to win Senate seats despite attracting a tiny number of votes need to be overhauled before the next federal election, the Greens say.

Greens senator Lee Rhiannon says voters should be given the option of allocating their own preferences above the line when they head to the polls this year.

"We need to change the system so it's voters that decide their preferences and we end the backroom deals," she told ABC radio on Friday.