The European Union is concerned about news that several Latin American countries are to reclaim control over their natural resources.
Deutsche Welle Radio says the latest is Bolivia, which this week announced that it is nationalizing REE, a power transmission company owned by a Spanish group.
President Evo Morales ordered the takeover at a May Day ceremony on Tuesday, saying that TDE (Transportadora de Electricidad) had not invested enough in Bolivia.
The European Commission said the move sent a negative signal to investors.
And Spain's economy minister Luis de Guindos said TDE had been providing Bolivians with a good service.
The company owns and runs around three-quarters of Bolivia's power grid.
''The Spanish government does not like such decisions, because they fail to provide legal security for Spanish capital investment in countries like Bolivia, Mr Guindos said.
''Actions like this one necessarily send a negative signal to international investors over the business and investment climate in Bolivia,'' he said.
However, Mr Guindos stressed that the case was very different from a decision by Argentina last month to nationalise YPF, an oil company in which Repsol of Spain had a controlling stake.