Critics say a new Indonesian law can protect legislators from investigations by the powerful anti-graft commission, triggering anger at what many regard as a grave setback for the world's third largest democracy.

The Law on Representative Assemblies, passed last month by the 560-member Parliament, came into force automatically after 30 days Thursday despite President Joko "Jokowi" Widodo's refusal to sign it because of public opposition.

Under the law, an investigation of any lawmaker must first be approved by the legislature's ethics council and then receive written permission from the president.

Jokowi suggested those opposed to the law could challenge it in the Constitutional Court.

Hundreds of students staged a protest Thursday outside the court, where some groups filed requests for a judicial review of the law.