SAO PAULO—The Brazilian real closed at its second-weakest level ever against the dollar on Monday as the country's political problems continue to worry investors, and shares declined.

The Ibovespa stocks index fell 2% to 43956 points. The real exited active trading at 4.0714 to the dollar, according to Tullett Prebon via FactSet, after closing at 3.9708 on Friday. Monday's was the real's second-weakest close against the dollar since the currency was launched in 1994.

The tension between President Dilma Rousseff, whose approval ratings have plummeted to less than 10%, and the country's Congress, which has yet to approve the government's package of austerity measures and has overturned some vetoes of spending measures, continues to spook investors, said Reginaldo Galhardo, a manager at the Treviso brokerage in Sao Paulo.

"The political situation is still generating a lot of uncertainty," he said. "The fight between Dilma and Congress is scaring people away."

The prospect of interest rate increases in the U.S. is also hurting the real, Mr. Galhardo said.

Concern about higher rates in the U.S. are affecting Brazilian shares as well, traders said. Iron-miner Vale SA was one of the biggest decliners in the Ibovespa on Monday, with a decline of 7.4% to 13.19 reais.

State-controlled oil company Petroleo Brasileiro SA, or Petrobras, declined 5.6% to 6.44 reais.

Write to Jeffrey T. Lewis at jeffrey.lewis@wsj.com

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(END) Dow Jones Newswires

September 28, 2015 18:05 ET (22:05 GMT)