Embattled Assistant Treasurer Kelly O'Dwyer has taken the extraordinary step of forcing Twitter to dismantle a social media "joke" account that compares her election campaign in Higgins to the disastrous 2013 loss of Indi by fellow Liberal Sophie Mirabella.

Meanwhile, former treasurer Peter Costello has rushed to Ms O'Dwyer's aid, sending a letter pleading with Higgins constituents to resist lodging a protest vote at the July 2 election.

Mr Costello, who held Higgins in Melbourne's inner south-east for more than 19 years, says in his letter that a protest vote against Ms O'Dwyer could leave Australia with a minority government similar to that "when Julia Gillard and the Greens were running things".