Andrew Tate and his brother Tristan are to be held in prison for 30 days.
Authorities raided the home of the former kickboxer and his brother in Pipera, at the northern edge of Bucharest, Romania.
Atena Observer reported that authorities were at the property for up to five hours and the operation is being headed up by the Directorate for Investigating Organized Crime and Terrorism (DIICOT).
DIICOT released a statement, saying: "The prosecutors of the Directorate for the Investigation of Organized Crime and Terrorism - Central Structure together with police officers from the Bucharest Organized Crime Brigade implemented 5 home search warrants in a case in which investigations under the aspect of committing the crimes of constituting an organized criminal group, human trafficking and rape."
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According to DIICOT, six people have been identified in relation to the investigation, one of whom is said to have been violently sexually assaulted in March.
Some of the suspects allegedly used the 'loverboy' method of trafficking, which involves a man luring a victim into a relationship in order to sexually exploit them later, DIICOT said.
The victims were transported and housed in buildings in Ilfov county, which surrounds Bucharest, where they were coerced into making pornographic content, it is alleged.
DIICOT released a video of the raid showing guns, knives and money on display in one room.
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A tweet was posted later on Friday on Tate's Twitter account saying: "The Matrix sent their agents."
The post was the latest in a series of 'matrix' references made by Tate, apparently linked to the movie franchise which depicts a fictionalised world in which humanity is trapped in a simulated reality.
The concept of the films has been co-opted by far-right conspiracy theorists and men's rights groups in recent years.
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Since retiring from combat sports, Tate, 36, has received attention for his misogynistic comments on social media.
In 2016, he was removed from Britain's version of the Big Brother TV show over a video that appeared to show him hitting a woman with a belt.
The following year, he was banned from Twitter for saying women should 'bear responsibility' for being sexually assaulted, but was reinstated last month.
Earlier in the week, Tate sparked a war of words with climate activist Greta Thunberg when he shared a picture of himself standing next to a Bugatti and claimed he owned 33 cars.
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"Please provide your email address so I can send a complete list of my car collection and their respective enormous emissions," he tweeted, tagging Thunberg.
She replied: "Yes, please do enlighten me. email me at [email protected]."
Tate and his brother have been under investigation since April alongside two Romanian nationals.
Jake Massey