Bolivia's military is on alert as four provinces prepare to formally declare their autonomy Saturday.
Santa Cruz, Tarija, Beni and Pando, relatively wealthy states in the eastern lowlands, have announced they intend to create largely independent regional governments.
Authorities have sent 400 police officers to Santa Cruz to ensure security during the challenge to the Bolivian government.
The provinces object to President Evo Morales's moves to overhaul the constitution to boost presidential powers and increase the rights of Bolivia's indigenous majority. Indigenous Bolivians live mainly in the more impoverished western highlands and form the core of Mr. Morales's support.
Mr. Morales, Bolivia's first indigenous president, wants to break up the large landholdings of the eastern farmers, many of whom are of European descent, and redistribute the property among indigenous groups.
He also wants to redistribute the nation's oil and gas wealth, which is centered in the east.
The four provinces are seeking to keep much of the tax revenues they generate. They say they do not want independence, but to retain control of their wealth.
Leaders in the region object to a Morales-backed constitution, approved Sunday in a vote boycotted by opposition lawmakers. The constitution would be put to a referendum next year.
The United States has urged Americans to defer travel to Bolivia.
Some information for this report was provided by AFP and AP .