Former Greens leader Bob Brown is appealing to Canberra voters not to let Katter's Australia Party get a hold of the Senate.
In a mass letter emailed on Tuesday to addresses across the Australian Capital Territory, Dr Brown says Canberrans are in a unique position with the power to prevent "homophobic hate from controlling the Senate".
The high-profile former senator, who is in a long-time, openly gay relationship, uses the letter to condemn Mr Katter and some of his party's candidates over recent controversial comments.
KAP Senate nominee Bernard Gaynor was dumped by the party last week after making anti-gay comments.
The party also forced out another candidate, Tess Corbett, who had linked gay rights to the acceptance of paedophiles.
But Dr Brown said such views were strongly held in Mr Katter's party and that present polling suggests the party could win some Senate seats.
He declares the ACT spot held by Liberal senator Gary Humphries to be
the most marginal Senate seat in the country, and one that should be used to counter the presence of the far right from other states.
Those elected to the Senate from the ACT take up their seats immediately following the election.
''Yet again, my namesake Bob (Katter that is) and his fellow travellers in Katter's Australia Party have been spreading a message of hate and fear towards gay and lesbian Australians,'' Dr Brown writes.
''It's one thing for Katter's party to hold these backward views. It's quite another to come to terms with the polling numbers showing that these people are on track to sharing the balance of power in the Senate with Tony Abbott's Liberals and Barnaby Joyce's Nationals.''
The former Greens leader goes on to explain that by voting in Greens candidate Simon Sheikh, the ACT could have an immediate impact on the Senate.
''What many haven't yet realised is that this year, Canberrans have the power to stop Katter's Australia Party in their tracks,'' he writes.
''Simon Sheikh is running with the Greens in the most marginal Senate race in Australia - and the choice in Canberra is between Simon and the Liberals.
''If we can get Simon elected in Canberra, we could stop the likes of Katter's Australia Party gaining control of the Senate alongside Abbott's Liberals.''
Mr Gaynor is fighting his suspension from the KAP for saying: ''I wouldn't let a gay person teach my children and I am not afraid to say it.''
He said Mr Katter privately agrees with his stance against gay teachers but had publicly caved into political correctness.
Dr Brown writes he knows what it is like to face hate and bigotry and it ''breaks my heart'' to see its impact on young people.
''This year's election we can decide whether Bob Katter's views remain on the margins - where they belong - or whether they'll be catapulted to the front and centre of Australian politics,'' he writes.
''It would be a sad day if Katter's Australia Party were successful in their attempt to grab the important responsibility of balancing the power of the old parties.
''We need leaders who bring out the best in people, not the worst. That's why it's so important we keep homophobic hate from controlling the Senate.''
Mr Katter did not respond.