Thousands of Bolivian peasant farmers have begun marching on La Paz, calling for ex-President Gonzalo Sanchez de Lozada to be put on trial.
The marchers blame him for the deaths of some 80 people last year in violent protests against government plans to export natural gas.
They also want Congress to give the state more power in the energy sector.
The march comes nearly a year after Mr Sanchez de Lozada, now in exile in the US, was forced to resign by the unrest.
The Bolivian Congress will meet on Wednesday to decide whether to open proceedings against Mr Sanchez de Lozada.
Two former members of the ex-president's cabinet may also face trial.
The marchers, who are being led by coca-growers' leader and opposition politician Evo Morales, are expected in La Paz at the weekend.
Bolivia has the second-largest natural gas reserves in Latin America, and economists say exporting gas is the only way to pull the country out of poverty.
But Bolivia's impoverished indigenous Indian majority believe the export plan will merely benefit the country's wealthy elite.
They want the gas to be nationalised and made available exclusively to the Bolivian people.
The latest protest over the future of Bolivia's gas industry comes just days before the 17 October anniversary of Mr Sanchez de Lozada's resignation from the presidency last year.
It also comes as his successor, Carlos Mesa, is facing a political backlash against his efforts to defuse the controversial gas issue.
In July, Mr Mesa won a five-point referendum allowing more exports of the country's lucrative natural gas reserves.
But the wording of the referendum was so complicated that the Bolivian Congress has been able to put forward a very different interpretation of what it meant.
The economic development committee has now rewritten the government's draft energy bill, imposing harsher taxes on foreign companies investing in Bolivia's energy sector.
Government ministers have warned that if the bill passes in its present form, it will mean an end to all foreign investment.