The Australian Sex Party has been deregistered for having less than 500 members, the Australian Electoral Commission has announced.
But Robbie Swan, registered officer and co-founder of the Sex Party, has said the party will "vigorously appeal" the decision.
"Since the party formed in 2009, we have had 6,000 people sign a statutory declaration on the bottom of a membership form, to say they want to be party members," he said.
"Without in any way criticising the staff at the AEC or their abilities to perform the job, they are being asked to use the most ridiculous methods to determine whether 500 bona fide members exist."
To discern the number of party members, the AEC contacts a sample of people who are both registered as party members and on the electoral roll. If a certain percentage of those people do not confirm their membership, the party is thought to have less than 500 members.
According to the Australian Sex Party, the AEC phoned a sample of 26 people before concluding the party had less than 500 members.
A spokesperson for the AEC told BuzzFeed News they had provided notice to the Australian Sex Party in March that deregistration was a possibility.
The spokesperson added that a party being deregistered means candidates cannot have the name of their party alongside their name on the ballot.
However, the Australian Sex Party has only lost its federal party status, meaning people can still run as Sex Party candidates at a state level.
The Australian Sex Party has been deregistered - http://t.co/XVabbPHe4Y #auspol
Mr Swan said the current methods of counting members were "gaming the system" against minor parties.
"The Sex Party is also at a disadvantage in that the majority of our membership is from young people who change their addresses frequently, do not have land line phone numbers and are much more transient than established Labor, Liberal or Green members."
"Minor parties need to be able to send in larger lists than the major parties who spend time and money making sure they send foolproof lists."
Australian Sex Party members have started posting pictures of their membership cards on social media in protest.
@AusElectoralCom I am a member of the Australian Sex Party.
My coveted @aussexparty membership - 6969
Hello @AusElectoralCom this is my @aussexparty membership. You never called or emailed. #auspol