Rights groups have also decried the legal proceedings as chaotic, confusing and farcical.

While some of the 24 are charged with spying and forgery, others are accused of illegally listening to radio frequencies.

And while some understand which charges they face, others remain in the dark because they are listed in official documents by number, and not name, according to Human Rights Watch – one of the many organisations that have criticised the trial.

All the defendants, who hail from several different countries including Greece, deny the charges against them.

The case, which has been ongoing for years and could take months to conclude, is part of a worsening battle between Greek authorities and civil society.

Since the height of the refugee crisis, Greece, which has taken in thousands of people fleeing war and poverty over the years, has increasingly cracked down on and scrutinised groups and activists, alleging some have aided smuggling. Meanwhile, rights groups have accused Greek authorities of mistreating refugees and illegally pushing them back at sea.

Among the accused in Tuesday’s trial is Sarah Mardini, the sister of the Olympic swimmer Yusra Mardini.

The Syrian siblings were celebrated for their efforts to save 18 fellow passengers when they helped drag their sinking refugee dinghy to safety on the journey from Turkey to Greece in 2015. Their story was later turned into the Netflix film, “The Swimmers.”

Yusra went on to swim in the Olympics in Rio de Janeiro in 2016, and Sarah, after receiving refugee status in Germany, returned to Lesbos to volunteer with refugees arriving on the island’s shores.

“I thought I could offer something there. It was a passion for me just to be there for other people,” Sarah said in a recent interview of her time volunteering on the Greek island.

In August 2018, however, she was arrested along with Seán Binder, a German citizen, when both were working for the ERCI (Emergency Response Center International) NGO, a search and rescue group.

Mardini and Binder were held in pre-trial detention for 106 days before being released.

Greek authorities allege that Mardini and Binder were among those who have monitored Greek Coast Guard radio channels and used a Jeep with fake military plates.

Mardini could face up to eight years in prison for the charges of espionage.

The spying allegations refer to the defendants’ use of an “encrypted messaging service” – the popular communication app, WhatsApp.

The Greek government had not responded to Al Jazeera’s request for comment at the time of publication.

The 24 defendants also face a separate investigation, in which they have not yet been charged, on allegations including smuggling and money laundering. On those charges, they could face up to 25 years in jail.

‘Unfair and baseless accusations’

Tuesday’s proceedings concern the misdemeanour charges and is the second attempt to hold a trial. The first was abruptly adjourned in November 2021 when the court realised it did not have jurisdiction over one of the defendants, a lawyer, and had to hand the case to a court with a higher authority.

Mardini, who was previously banned from entering Greece, will not attend court.

Binder, who will be present, said there still appears to be serious issues with the case, citing a missing page of the indictment.

“If we are found guilty of spying because we used WhatsApp, if we are facilitators of illegal entry because we did search and rescue, if we are money launderers because we worked as a charity, then anybody who does search and rescue who works in a charity, or who uses WhatsApp will be guilty of these crimes,” he said, adding that the case has had a chilling effect on humanitarian work in Europe.

Giorgos Kosmopoulos, senior campaigner on migration at Amnesty International told Al Jazeera: “Sarah and Sean’s ordeal speaks volumes about Greece’s efforts to keep refugees and migrants away by any means and how that also includes those who would help them in an hour of need.

“The accusations they face are unfair and baseless and should be dropped so they can carry on with their lives.”

Comparisons have been drawn between the Greek episode and ongoing prosecution of members of the Iuventa search and rescue ship in Italy, where NGO workers face up to 20 years in prison for “facilitating illegal immigration.”

“This is an official attempt to criminalise humanitarian assistance,” Zacharias Kesses, Mardini and Binder’s lawyer told Al Jazeera. “The police created a totally chaotic criminal file with no evidence at all, only based on arbitrary assumptions.

“They keep on renaming humanitarian assistance as facilitation of migrant smuggling.

He highlighted the impact on some defendants, saying: “Lots of time has been lost and many people have been traumatised and have a serious problem going on with their lives.”

‘Illegal pushbacks’

Bill Van Esveld, associate children’s rights director at Human Rights Watch, said the case had “turned laws and facts on their heads and placed the liberty of humanitarians from across the European Union at stake.”

“Search and rescue has all but stopped in Greece and we have seen multiple reports showing the Greek authorities illegally pushing refugees back to Turkey,” said Grace O’Sullivan, an Irish member of the European Parliament who has travelled to Lesbos for the trial.

Greek authorities have denied involvement in illegal pushbacks, which have been documented by rights groups and journalists.

O’Sullivan said she hoped the authorities would “throw these ridiculous charges out as a first step”.

She is one of more than 80 politicians in the European Parliament who have signed a letter in support of the defendants.

“[It’s] a threat to all of us and a threat to the idea of the ‘so-called’ European values,” said Binder, who was raised in Ireland. “I think that there’s a lot more at stake [here] than a group of 24 humanitarians.”

The trial is expected to begin at around 9am (07:00 GMT).