The Bolivian lower house of Congress has approved a law giving indigenous communities the right to administer their own justice systems.
The government says the measure, which now goes to the Senate, will allow indigenous groups to settle disputes according to their own cultural values.
But opposition parties have warned that it could lead to mob rule.
Last month four policemen were lynched by an Andean clan in the name of indigenous justice.
Their bodies were handed over to relatives ast the weekend.
Members of the so-called Warrior Clans returned the bodies after demanding a promise that charges would not be filed against them.
They accused the policemen, who belonged to a unit tackling car theft, of extortion.
The area - in the province of Potosi - is a well-known smuggling route for cars from neighbouring Chile.
The Warrior Clans hid the bodies and refused to release them, demanding that police investigate the deaths of four of their members.
Officials have agreed to investigate some of the complaints.