Divisive internet personality Andrew Tate, his brother and two other suspects were ordered late on Tuesday to remain in Romanian police custody for 30 days pending a criminal inquiry into alleged human trafficking.
Romanian anti-organised crime prosecutors detained Tate, his brother Tristan and two Romanian female suspects on December 29 on charges of forming a criminal gang to sexually exploit six women.
They have denied wrongdoing through their lawyers and challenged the 30-day arrest warrant. On Tuesday, the Bucharest Court of Appeals said it rejected the challenge as "unfounded".
"Prosecutors' arguments were that they have evidence. Naturally, our arguments were that there isn't evidence," said Ioan Gliga, one of the defence lawyers.
The first court to issue the arrest warrant said there was a risk that the suspects could evade justice by leaving Romania for countries with which Bucharest had no extradition treaty.
Prosecutors have said the Tate brothers recruited their victims by seducing them and falsely claiming to want a relationship.
They said the victims were then taken to properties on the outskirts of the capital Bucharest and through physical violence and mental intimidation were sexually exploited.
They were forced to produce pornographic content for social media sites, generating large financial gains, prosecutors said.
They also said one of the brothers raped one of the victims in March of last year, which is when the investigation started.
Prosecutors have seized 15 luxury vehicles and more than 10 properties and homes belonging to the suspects in Bucharest and Prahova and Brasov counties, Ramona Bolla, a spokeswoman for Romania's Diicot anti-organised crime unit, told Reuters.
The seizure was meant to prevent the assets being sold or concealed.
Andrew Tate arrested in Romania over human trafficking case - video
Should prosecutors need more time to investigate, they can seek approval for further extensions of up to 180 days of detention under Romanian law.
Tate gained mainstream notoriety for misogynistic remarks and hate speech that got him banned from all major social media platforms, although his Twitter account was reinstated in November after Elon Musk acquired the social media giant.
The former professional kickboxer, who holds US and British nationality, has said women are partly responsible for being raped and that they belong to men. He is a self-professed misogynist.
On a podcast last year, he said he started making money by convincing girlfriends to videochat and share the profits back when he lived in London.
"How can I use these women to make me money?" Tate said.
He said his business started with two girlfriends and peaked with 75 women working for him and earning $600,000 a month.
Tate has also said he moved to Romania after being investigated in the UK on charges of sexual assault, which were ultimately dropped, because he liked living in countries where corruption was accessible to everyone.