Three men and a woman have denied charges of human trafficking and forcing women into prostitution.
Vojtech Gombar, 61, Anil Raj Wagle, 37, Jana Sandorova, 28, and Ratislav Adam, 31, appeared at the High Court in Glasgow on Tuesday in relation to a combined 29 charges. All are from Glasgow.
More than 13 women are said to have been trafficked, mostly from Slovakia, to be exploited in the UK or elsewhere.
Money is alleged to have been transferred between different parties for control of women to be forced into sex work, with removal of identity cards and threats of violence.
The court was told the four discussed taking "ownership" of at least four other women from Slovakia, before deleting the correspondence.
The accused are said to have worked from at least three properties in Glasgow, as well as premises around the UK, France, Slovakia and Ireland.
Family members of the alleged victims were threatened and parents were paid for control of their daughters, the court was told.
Gombar faces 24 charges, Wagle faces six, Sandorova faces 11, and Adam faces 16, all of which they denied.
The crimes are alleged to have taken place between November 2011 and February 2017.
Judge Lord Beckett warned the jury the trial could be "a bit untidy and ragged at times" due to evidence having to be heard from Slovakia.
He added that technical difficulties with video links and different judicial procedures could add to delays.
The trial is set to resume on Wednesday and is expected to last four to 10 weeks.
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