With about 45 days remaining before a major post-9/11 surveillance authorization expires, representatives of the National Security Agency and the FBI are taking to Capitol Hill to convince legislators to preserve their sweeping spy powers.

That effort effectively re-inaugurates a surveillance debate in Congress that has spent much of 2015 behind closed doors. Within days, congressional sources tell the Guardian, the premiere NSA reform bill of the last Congress, known as the USA Freedom Act, is set for reintroduction – and this time, some former supporters fear the latest version of the bill will squander an opportunity for even broader surveillance reform.

Republican leaders of the House intelligence committee arranged for NSA and FBI representatives to hold secret briefings for members of Congress on Tuesday and Wednesday. Staff did not name the officials addressing legislators.