WASHINGTON (Reuters) - The U.S. Senate has reached an agreement to approve the reauthorization of a controversial surveillance program and plans to vote on it on Friday night, Senate Majority Leader Chuck Schumer said.

If the Senate votes to reauthorize the Foreign Intelligence Surveillance Act, which the House approved last week, it would secure what supporters call a key element of the United States' foreign intelligence-gathering operation. The law is set to expire at midnight Friday.

"It's an important part of our national security toolkit and helps law enforcement stop terrorist attacks, drug trafficking, and violent extremism," Schumer said in a written statement.

FISA has attracted criticism from both Republican and Democratic lawmakers, who argue it violates Americans' constitutional right to privacy. The bill was blocked three times in the past five months by House Republicans bucking their party, before passing last week by a 273-147 vote when its duration was shortened from five years to two years.