The Liberal Party is battling to hold a third Senate seat in Western Australia in Saturday's historic byelection for the upper house as an advertising blitz from mining magnate Clive Palmer begins to bite.

Polls - albeit with a small sample size - are suggesting the Palmer United Party has doubled its vote to 10 per cent, enough with preferences to get a Senate position.

On his jet: Clive Palmer is making an impact in the Western Australia byelection. Credit:Jay Cronan

At stake is the ability of the Abbott government to pass legislation through the Senate. A loss of an upper house seat would mean the Coalition needs an extra seven votes.

If the Palmer United Party picks up a Senate position, it will have three senators and the support of Ricky Muir from the Motoring Enthusiasts' Party, likely to be enough for him to block legislation with Greens and Labor.