A measure granting the government expansive power to intercept electronic communications in the United States without a warrant is set to expire this month, setting up a sharp debate in the Senate over how to balance privacy against national security.

The government uses the measure, contained in a law known as the FISA Amendments Act, to intercept emails and telephone calls of foreigners located overseas under a blanket approval issued once a year by a special court. But communications of U.S. citizens talking with the foreigners also are being scooped up.

The intelligence community argues that the measure is essential to protect against foreign threats and has made renewing the law its top legislative priority. The House of Representatives approved a five-year extension in September by a vote of 301 to 118. The Senate must vote by the end of the year or the authority will expire.