A heterosexual couple, Lucy Hilken and Tim Garrett, had their application for a civil partnership refused at Aldershot Register Office on Tuesday 14 December.
The registrar cited the legal ban on opposite-sex civil partnerships as the reason for the rejection.
The couple now plan to commence legal action in the courts, together with seven other couples who have been similarly refused.
The joint legal action is scheduled to be launched in the Great Hall at King's College London at 10am on 21 December.
Commenting on the latest refusal, Tim Garrett (aged 31) said: "We are disappointed but not surprised by the refusal to grant us a civil partnership. The register office staff were very courteous and helpful. But the legislation they currently have to abide by is outdated and discriminatory. The thinking behind the ban is anachronistic and reminiscent of the days of whites-only golf clubs and such like."
"We hope Britain will soon join other civilised, liberal democracies such as South Africa and the Netherlands, by casting off this unpleasant and offensive form of segregation. Allowing civil partnerships only to gay people and civil marriages only to straight people is unjust discrimination," he added.
Garrett partner Lucy Hilken (also aged 31) commented: "I don't see any valid justification for the law to deny us the right to register our relationship as a civil partnership. We want legal recognition of our commitment to each other, not only for ourselves but for the sake of our daughter. We have been refused a civil partnership on unfair and discriminatory grounds."
Mr Garrett and Ms Hilken are both teachers. They have been in a relationship together for 11 years and have a young daughter. Their application was part of the Equal Love campaign (www.equallove.org.uk), which seeks the repeal of the twin prohibitions on gay civil marriages and heterosexual civil partnerships.
A total of eight couples who have filed applications at register offices across the country, in a bid to overturn the "sexual segregation" in civil marriage and civil partnership law. They are the fourth straight couple to challenge the ban on heterosexual civil partnerships. Four same-sex couples have applied for civil marriages and have also been rejected.
The Equal Love campaign is being organised by the gay rights group OutRage! with the support of the Peter Tatchell Human Rights Fund.