Workers in Bolivia are threatening an indefinite general strike next month in a renewed bid to halt the government's plan to export natural gas.
Bolivia's natural gas is not for sale, say protesters
The main trade union federation, the COB, gave President Carlos Mesa until 1 May to change his policy on the gas export plan or face fresh unrest.
Violent protests over the proposals brought down Mr Mesa's predecessor, Gonzalo Sanchez de Lozada, last year.
Opponents say Bolivia's gas is for the use of Bolivians, not foreigners.
They want the government to nationalise the country's gas reserves - the second-largest in Latin America.
Otherwise, they fear that proceeds from the gas will simply enrich foreign companies investing in the project.
President Mesa has announced a referendum on the export plan to be held on 18 July in an effort to defuse the controversy, which prompted a major cabinet reshuffle on Tuesday.
Earlier plans to export the gas through Chilean ports on the Pacific coast angered nationalists, because the ports belonged to Bolivia before the 1879 war with Chile.
The government has now said it favours using Peruvian ports instead.
However, the trade unions oppose the possible sale of Bolivian gas to Argentina, fearing that it might be re-exported to Chile.
In the latest demonstrations against the export plan, thousands of workers marched through the streets of La Paz and other major cities on Thursday, shouting, "The gas is not for sale."
They called on the government to change its economic policies or face a general strike from 3 May, backed by peasant farmers and a campaign of roadblocks.
COB leader Jaime Solares said that President Mesa "will be responsible for whatever happens in the country" if he did not heed the protesters' call.
The latest turmoil comes six months after President Sanchez de Lozada resigned in the wake of violent protests over the gas issue, in which some 80 people were killed.