The FBI and Silicon Valley are in a fight over whether web browsing records are the same as telephone bill records.

The latest surveillance battle gripping the technology industry is focused on a rewrite of US surveillance law that would mean the justice department would be able to access a citizen’s web browsing history, location data and some email records without approval from a judge using a so-called “national security letters” (NSLs).

The FBI contends that such data is covered implicitly under current statute, which was written years ago and only explicitly covers data normally associated with telephone records.

Director James Comey now is lobbying Congress to make clear it also applies to the digital equivalent.

Late on Monday, major technology companies including Google, Facebook and Yahoo sent a letter warning Congress that they would oppose any efforts to rewrite law in the FBI’s favor.

“This expansion of the NSL statute has been characterized by some government officials as merely fixing a ‘typo’ in the law,” the companies wrote. “In reality, however, it would dramatically expand the ability of the FBI to get sensitive information about users’ online activities without court oversight.”

It marks another battle over a small clause in federal law that could dramatically affect how the US conducts terrorism investigations. For years, the bureau has relied on the controversial national security letters to obtain certain types of data quickly from technology companies. These letters don’t require a warrant and often come with a gag order prohibiting the recipients from discussing them. Technology companies complain the FBI has become too reliant on them, but the FBI complains that cases are getting slowed down because some companies have stopped cooperating.

It’s not so much that technology companies don’t want to give any user data to the government. Rather, their legal teams have problems with the growth of national security letters because the accompanying gag orders prevent companies from telling users much about how they help the government. This can create mistrust and, as happened after the Edward Snowden leaks, eventual embarrassment if the details are disclosed.

Companies also argue NSLs are problematic because of the lack of judicial oversight. They give too much power to one branch of government, they argue, and make it hard to predict what the government may ask for next.

Comey has said expanding NSL rules is one of his agencies top legislative priorities. US senators are exploring multiple ways to pass the law tweak this year.

Technology and legal experts also dispute Comey’s argument that he effectively is asking Congress to correct a typo. In 2008, the justice department’s office of legal counsel said explicitly that the agency can only issue national security letters for “name, address, length of service, and local and long distance toll billing records”.

At the time, the government had asked DoJ’s lawyer if those four types of data are “exhaustive or merely illustrative of the information that the FBI may request and a provider may turn over”.

To which the office of legal counsel responded: “We conclude that the list ... is exhaustive.”