The Malaysian opposition leader, Anwar Ibrahim, was charged on Tuesday for participating in an electoral reform rally last month.
Two fellow members of the People's Justice Party were also charged with violating a new law that overseas public gatherings.
The rally, held in Kuala Lumpur, was banned by court order.
Tens of thousands of Malaysians joined the rally, demanding electoral reform, and protesting against what they said was a corrupt electoral process, which favoured the ruling coalition.