Marine Le Pen, the French far-right party leader, has gone on trial accused of misappropriating EU funds.
Ms Le Pen, who has insisted she has committed no wrongdoing, is accused of using money intended for EU parliamentary work to pay staff working for her party.
Also accused are 24 others and the National Rally (RN) party itself.
The European Parliament has estimated the damage at 3.5 million euros (£2.92million), its lawyer Patrick Maisonneuve said.
The trial could potentially be damaging for Le Pen, who risks being barred from public office for several years if found guilty.
Ms Le Pen claimed before the trial began that her and her party’s use of the money was legitimate.
"I approach this trial with great peace of mind," she told reporters as she arrived at the criminal tribunal in Paris.
If cleared of wrongdoing, political analysts say it could boost Ms Le Pen and her party ahead of the 2027 French presidential election.
The 56-year-old, who lost to Emmanuel Macron in the second round of France's presidential election in 2017 and 2022, is widely seen as a frontrunner for the 2027 race.
EU lawmakers are allocated funds to cover expenses, including their assistants, but are not meant to use them to subsidise party activities.
Party spokesman Laurent Jacobelli said the RN had "a different understanding, as a French party, of what an assistant role is, compared with the European Parliament's understanding.”
Ms Le Pen, an MEP in Brussels from 2004 until 2017, is facing charges both for her role as party leader and as an EU lawmaker at the time, for allegedly hiring fictitious assistants herself.
If found guilty, she and other defendants could face a potential jail sentence of up to 10 years and a one million euro (£835,000) fine.
In addition, those who were elected officials at the time of the alleged offences risk being barred from public office for up to ten years.
Her father, Jean-Marie Le Pen, 96, was also among the accused, but he is set to be judged at a later stage after a judge recused him from current proceedings on health grounds.
The trial will last until November 27.
Ms Le Pen’s party is known for advocating a far-right hardline stance on immigration and a populist right-wing agenda which it calls “France first”.
