US intelligence officials are fighting to renew the controversial spying program which allows agencies to conduct bulk surveillance on internet users.

Section 702 of the Foreign Intelligence Surveillance Act gives US intelligence permission to spy on and store internet data and communications of foreign people living outside the US.

The George W Bush-era program’s authorization is set to expire on December 31 if Congress doesn’t renew it. The Senate Intelligence Committee is expected to privately vote on a bill to reauthorize the law on Tuesday, despite requests to hold the debate in public.

Meanwhile the Senate Intelligence Committee is debating this law in secret today. I objected to that: pic.twitter.com/kfocN9QePG — Ron Wyden (@RonWyden) October 24, 2017

Former directors of national intelligence, the CIA and the NSA have penned a letter pushing for Congress to allow the sweeping, warrant-free eavesdropping to continue.

READ MORE: Tech giants call for privacy protections in surveillance reform

“We strongly urge the Congress to reauthorize the program and continue allowing the intelligence community to protect our country,” the former intelligence chiefs said.

The group said it had “personally reported” to presidents and Congress “details of plots disrupted based on information from Section 702.”

The letter’s signatories include former heads of the CIA and the National Security Agency and a former attorney general. One of the signatories is former Director of National Intelligence James Clapper, who, in 2013, told a Senate intelligence committee that the NSA did not “wittingly” collect data on Americans.

GOP & Dem lawmakers introduce 1st bill to limit warrantless surveillance https://t.co/OiUFvLlyaqpic.twitter.com/KvivumZQPW — RT America (@RT_America) October 5, 2017

The program has been widely criticized over its collection of Americans’ communications, which can be “swept up” among foreign communications and can then be searched without the need for a warrant. Those who aren’t American also object to being surveilled by a foreign government.

Some of the spying programs revealed by NSA whistleblower Edward Snowden which are included under Section 702 are PRISM and Upstream. PRISM sweeps up data from tech giants like Apple, Google, Facebook and Microsoft that’s sent to or from a foreign target.

READ MORE: FISA court finds NSA violated search restrictions, spied on Americans

Upstream is a form of bulk surveillance used to search internet traffic and communications as they are in transit via cables and routers. Americans who communicate with people overseas or use websites hosted on servers in other countries are exposed to the NSA’s bulk interception tool.

The NSA uses a wide range of “selectors” to search content. This can include any terms that are of interest to the spy agencies, and foreign targets’ email addresses, or any mention of that target or term made elsewhere. However, any foreign person believed to be in possession of “foreign intelligence information” can be a target, and that includes journalists, attorneys, and human rights workers.

Introduced the USA Rights Act today with @RandPaul and bipartisan coalition that knows liberty and security aren’t mutually exclusive. pic.twitter.com/gQoGHEAyD0 — Ron Wyden (@RonWyden) October 24, 2017

The question of the US’s ability to collect European data via tech giants is due to be debated in the Court of Justice of the European Union (CJEU). It centers around whether Facebook can continue to send European data from its Irish subsidiary to the US when it’s unable to prevent the NSA from spying on that data.

The CJEU already canceled the Safe Harbor data-sharing agreement between the US and the EU as a result of Snowden’s revelations, as it could not guarantee the safety of Europeans’ data.

A number of bipartisan lawmakers in the House of Representatives have introduced legislation that would add privacy protections under 702, including requiring the FBI to obtain a warrant before it accesses Americans’ data. The USA Rights Act was introduced by Ron Wyden and Rand Paul.