Update (1/17/2018, 2:25pm ET): The Senate broke the filibuster by a vote of 60-38 after just two-and-a-half hours of discussion Tuesday evening. This limits the debate on the FISA Amendments Reauthorization Act to a maximum of 30 hours. According to Rand Paul's press liaison it is "highly likely" the vote will occur Wednesday night or sometime on Thursday. Motherboard will update this post with the results.
On Tuesday afternoon, a bipartisan coalition of 3 Democrats and 2 Republicans committed to filibustering the FISA Amendments Reauthorization Act of 2017, a bill that effectively expands the warrantless surveillance of American citizens. Last week, the House of Representatives voted in favor of a nearly identical bill to the one being considered in the Senate today.
The filibuster coalition is led by Republican Senator Rand Paul and Democratic Senator Ron Wyden, who have co-sponsored the USA Rights Act, a privacy-oriented alternative to the FISA Amendments Reauthorization Act that is widely supported by civil rights groups.