Prominent Perth lawyer John Hammond says an event with free drinks and pizza to be hosted by Pauline Hanson's at a pub in Perth is a type of "electioneering" that's "unacceptable and unlawful."

Ms Hanson is due to appear at the Paddington Ale House in Mount Hawthorn on Thursday night, and the 'Pots & Pizzas with Pauline' event's advertising promises "free pizza and the first 100 drinks on her."

The One Nation leader is visiting WA in an eleventh hour effort to shore up support for her party, which is tipped to win the balance of power in the upper house, but is also beset with internal strife.

The event at the Paddington has stoked plenty of controversy, with the pub's Facebook events page swamped with both critical and supportive comments.