Venezuela has charged opposition leader Maria Corina Machado with plotting to kill President Maduro.
She and her supporters have denounced the accusations as politically motivated.
Machado was at the forefront of major street protests against Maduro’s socialist government earlier this year.
If found guilty, the former legislator could be sentenced to between 8 and 16 years in jail.
Prosecutors have claimed a series of emails revealed the alleged assassination plot by political opponents and US diplomats.
The opposition’s radical wing praises Machado for standing up to what they consider a dictatorship.
But she is loathed by many government supporters, who see her as an out-of-touch aristocrat intent on toppling the government.
Earlier this year Leopoldo López, a fellow opposition leader who along with Machado was one of the protest movement’s main figureheads, was jailed and is currently on trial accused of inciting violence.
The demonstrations lasted three months and resulted in more than 40 deaths.
President Maduro who succeeded Hugo Chávez has seen his popularity slump amid shortages of goods and soaring inflation.
Critics claim he is trying to silence opponents and distract Venezuelans from the economic crisis.
Some US politicians have called for more sanctions against Caracas.