The US Senate is set to vote on a bill that would expand FBI surveillance in the wake of a shooting at a gay nightclub in Orlando. As Reuters reports, Senate majority leader set up the vote Monday night by introducing an amendment to a criminal justice appropriations bill. The proposal would expand the FBI's authority to use "national security letters" (NSLs) to access a suspect's internet browsing history and email metadata without a warrant. A vote is expected on Wednesday.

The amendment has the support of leading Senate Republicans. "In the wake of the tragic massacre in Orlando, it is important our law enforcement have the tools they need to conduct counterterrorism investigations," Senator John McCain said in a statement.

"frightening and invasive"

But civil liberties groups have long criticized NSLs for their lack of transparency and oversight. The Electronic Frontier Foundation (EFF) describes NSLs as "one of the most frightening and invasive" surveillance powers that were expanded under the US Patriot Act.

NSLs are issued without judicial approval, and are typically accompanied with a gag order that prevents internet service providers from informing targets of the surveillance. In one case, an ISP that contested an NSL was only allowed to discuss after more than a decade.

The amendment would not allow the FBI to access the content of people's communications, though it would allow the agency to access their electronic metadata, including a list of websites they visit and IP addresses. A 2008 Justice Department memo said that NSLs are currently limited to phone billing information, and FBI Director James Comey has pushed lawmakers to expand their scope.

The amendment announced this week would also allow intelligence agencies to monitor so-called "lone wolf" suspects who do not have ties to terrorist groups. The lone wolf provision is already included under the Patriot Act and was extended until 2019, but the amendment would make it permanent. According to the Justice Department, the power has never been used.