London(CNN) The UK could become the next country to issue gender neutral passports if an activist trying to force the government to overturn its policy wins a court appeal on Tuesday.
Christie Elan-Cane has argued the UK's current passport process is "unacceptable," and breaches international human rights law. They are pushing the Home Office to allow an "X" gender option, alongside male and female.
Elan-Cane's original legal challenge was rejected last year by London's High Court, but their appeal is being heard on Tuesday.
A handful of countries, including Germany, Australia and Canada, already offer a third option, other than male or female, on their passports.
Elan-Cane argues that the government's current policy breaks the European Convention on Human Rights (ECHR) because it breaches the right to respect for private life and the right not to be discriminated against on the basis of gender or sex.
"Legitimate identity is a fundamental human right, but non-gendered people are treated as though we have no rights," Elan-Cane said in a statement ahead of the case.
"It is unacceptable that someone who defines as neither male nor female is forced to declare an inappropriate gender in order to obtain a passport," Elan-Cane added.
"X" is accepted as a gender entry on machine-readable travel documents, alongside "M" and "F," under standards set by the International Civil Aviation Organization.
But the British government has resisted calls from activists to change its processes.
A government lawyer argued that the current policy is needed to maintain an "administratively coherent system," to maintain security at national borders and to combat identity theft.
More than 80 British MPs supported the most recent Parliamentary motion calling for an "X" entry on passports.
Elan-Cane has protested gender-neutral issues for several years, and has also called for the government to include a third gender option on their next population-wide census in 2021.