President Evo Morales of Bolivia has ordered the nationalisation of four private electricity companies.
Police moved into the offices of Corani, Valle Hermoso and Guaracachi firms, following the decree.
Corani is half owned by a subsidiary of GDF Suez of France. Guaracachi's main partner is Rurelec of Britain, while ELFEC and Valle Hermoso are local.
Mr Morales said the government now controlled 80% of the country's electricity generation.
The BBC reports the four companies seized on Saturday account for more than half of Bolivia's electricity market.
Mr Morales nationalised the gas and oil industry in 2006 and the national telephone company in 2008. Those announcements were also made on May Day.