More than four years after they were arrested for carrying out migrant rescue missions on Greek island of Lesbos, the trial of 24 volunteers commenced on Tuesday but was later adjourned until Friday.

The 24 defendants, including several foreign nationals, worked for the now defunct NGO Emergency Response Centre International — a search and rescue group operating on the island of Lesbos from 2016 to 2018, they have been charged with facilitating illegal migration into the European Union, as well as other felonies.

Their case was denounced in a European Parliament report as Europe’s “largest case of criminalisation of solidarity”.

The volunteers were initially detained in 2018 for several months on suspicion of human trafficking, but the charges facing the group in court on Tuesday involved espionage, illegal access to state communications, money laundering and assisting criminal activity.

Police said in 2018 that the volunteers had collected information about refugee flows from the Turkish coast to the Greek islands of Lesbos and Samos, and provided direct assistance to organised trafficking groups.

Three of the defendants — Sarah Mardini, Sean Binder and Nassos Karakitsos, who were arrested in August 2018 — have already spent more than three months in pre-trial detention. The case was supposed to go ahead in 2021 but was delayed over procedural issues. Human rights monitors decried the slow proceedings and said the case was politically motivated.

Human rights group Amnesty International has called the case against the aid workers as “farcical” and demanded Greek authorities drop the charges.

A group of European Parliament members have signed a letter calling on the government in Athens to drop the case.