A trans woman suing after being blocked from a women-only social media platform has been backed by the Australian Human Rights Commission in her case.
Roxanne Tickle is suing Giggle for Girls in the Federal Court after having her access to the app revoked in September 2021.
Maintaining her appearance as a woman since 2017, Ms Tickle underwent gender-affirming surgery in October 2019 and was issued a birth certificate stating she was female the following year.
Giggle for Girls, which cites itself as "made for women by women", blocked Ms Tickle in 2021 after considering her male.
After the platform failed to get the lawsuit thrown out in June, the AHRC was called on as a "friend of the court" to make submissions on whether Ms Tickle's case was validly brought.
Sex Discrimination Commissioner Anna Cody dismissed Giggle for Girls' arguments that sex was a biological, binary characteristic under which someone could simply be classified as either a man or a woman.
"'Sex' can refer to a person being male, female or another non-binary status," she wrote.
"It is also broad enough to encompass the idea that a person's 'sex' can be changed."
To determine whether someone was female, a court merely needed to determine what their birth certificate stated and, if trans, they had undergone gender-affirming surgery.
"At least as early as the 1990s, it has been accepted that 'sex' is changeable and that the female 'sex' includes a person who has undergone gender-affirming surgery to affirm their status as female," Ms Cody wrote.
In making the submission, she rejected Giggle for Girls' claims the lawsuit should have been filed as a sex discrimination case, saying the allegations were actually of gender identity discrimination.
"A trans woman may say that her gender identity is female, but (the Sex Discrimination Act) would still protect her from direct discrimination on the ground that she was identified by the discriminator as a trans woman and was treated less favourably than a person with a different gender identity as a result."
Giggle for Girls' claims it could dodge the lawsuit because it was a "special measure" put in place to help women avoid discrimination were also rejected.
Under such measures, marginalised groups can receive preferential treatment to achieve equality.
Ms Cody said the social media platform was a special measure that could not be sued for sex discrimination but gender identity claims could still be brought against it.
"A person who aims to achieve substantive equality between men and women should not also be permitted to engage in discrimination against persons with a certain gender identity," she wrote.
The commissioner also dismissed Giggle for Girls' claims that parts of the act regarding gender identity and the definition of "sex" were constitutionally invalid.
In a statement filed with the human rights commission in December 2021, before the Federal Court case was launched, Ms Tickle outlined the alleged discrimination.
"I believe that I am being discriminated against by being provided with extremely limited functionality of a smart phone app by the app provider compared to that of other users because I am a transgender woman," Ms Tickle wrote.
"I am legally permitted to identify as female."
Giggle and its chief executive Sally Grover did not know Ms Tickle was transgender and it did not inform the decision to revoke her access, lawyers wrote in response to the complaint in March last year.
Ms Grover described Ms Tickle as a "trans-identified male" in a social media post less than three weeks later.
She added that Ms Tickle wanted her to be "re-educated".
Ms Tickle is seeking damages, a written apology and restored access to the platform.
The case has been set down for a four-day hearing in April next year.
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