Sen. Richard Ferracdo said when a phone call to the president was intercepted, "it is difficult to imagine what might be happening," O Globo reported Monday.
O Globo reported Sunday that the U.S. National Security Agency monitored phone calls, emails and cellphone messages of President Dilma Rousseff and an undefined number of "key advisers" within the Brazilian government.
Ferracdo said it was "unacceptable" for spying to occur in a country "where there is no atmosphere of terrorism."
He called upon his government to investigate and demand an explanation from the U.S. envoy to Brazil, O Globo said.
The monitoring was revealed information passed along to Glenn Greenwald, a reporter for Britain's The Guardian living in Brazil, by former NSA contractor Edward Snowden, who was granted temporary asylum in Russia.