A long-awaited trial of 24 members of humanitarian organizations began on Tuesday on the Greek island of Lesvos.
They are accused of smuggling, espionage and money laundering.
Among the accused is the Syrian refugee helper Sarah Mardini.
She is represented by lawyers, state radio reported.
Scores of members of three non-governmental organizations (NGOs) have been accused of smuggling on the east Aegean island of Lesvos.
According to the police, they have systematically supported the crossing of migrants from Turkey to Greece.
They illegally intercepted police and coast guard radio communications and passed on the positions of coast guard boats and ships to migrants who wanted to cross from Turkey to Greece and thus to the EU.
The defendants' defense lawyers characterized these allegations as a "farce".
The police became aware of the activities of one of the NGOs when, in February 2018, they arrested two of their members who were driving on Lesvos in a vehicle with fake Greek army license plates.
This was followed by months of investigations and observation by the NGOs.
Sarah Mardini has become known to a wider audience through the current Netflix drama "The Swimmers".
The film by director Sally El Hosaini tells the story of the sisters Sarah and Yusra Mardini, who made headlines in 2015: At that time, the two swimmers are said to have pulled a refugee boat behind them for hours with a rope that was in distress off the island of Lesbos.
After that, the two settled in Germany.
It is unclear how long the trial will last, lawyers for the defendants said on the radio.