A growing number of technology companies seeking to promote transparency have been testing the limits of new government guidelines on how they can disclose national security orders for their customers’ data.

Over the past year or so, about a dozen online and communications firms have reported that they have never received such a request, effectively breaching the spirit if not the letter of government guidance issued in January intended to make it more difficult for would-be terrorists or spies to identify services that could be used to evade detection. Their decisions have frustrated U.S. officials, even as they privately acknowledge there is little they have been able to do about it.

The right to report zero is part of a broader tussle between the private sector and the government over transparency and the proper boundary between free speech and national security.

In October, Twitter sued the government, charging that its First Amendment rights were squelched when the Justice Department blocked it from publishing a transparency report that sought to disclose the specific number of orders it had received and the fact that the number was limited. The firm also alleged that preventing a company from reporting “zero” national security requests is an unconstitutional restraint on speech.

The guidelines take the form of an agreement reached with five major tech companies that allowed for reporting of government national security requests in broad ranges, such as 0-999. There is no “zero” option.

While technology companies say their customers have a right to know how often the federal government requests data as part of national security investigations, officials say detailed disclosures will aid suspected terrorists and other potential surveillance targets.

“The dilemma,” said a former senior Justice Department official, “is where do you draw the line between the justifiable need of companies to give their customers an accurate picture of when they’re turning over information to the government about them and, on the other hand, the justifiable need of the government to not telegraph to the bad guys where it is or is not looking?”

A Justice Department spokeswoman declined to comment for the story, citing the pending litigation.

Officials say the guidance, practically speaking, can apply only to a company that has received at least one order, whether it is a national security letter — an administrative subpoena for customer data — or a wiretap order issued by a judge under the Foreign Intelligence Surveillance Act. Both come with nondisclosure provisions.

“I think you’d have a First Amendment issue on your hands if you tried to preclude someone who hadn’t received something from saying they hadn’t received it,” said one official, who spoke on condition of anonymity to discuss a sensitive topic.

Among the companies that have taken the “zero option” in their transparency reports are Tumblr, a blogging and social media platform, and Pinterest, a social networking site that lets users share images on digital pinboards.

The firms call such notices “warrant canaries,” a term inspired by the proverbial “canary in a coal mine,” whose death alerted miners when dangerous gases had accumulated. When a warrant canary is removed from a report, the company is signaling a request has been received.

“If the government is going to a company to find out information about you, then the company should do everything in its power to let you know about that,” said Eric Gundersen, chief executive of Mapbox, a Washington-based startup that put a warrant canary in its transparency report in October. “This is about respect for your customers. The government can’t use companies to shield them after requesting customers’ personal information.”

Some firms began issuing warrant canaries shortly after the first disclosures by former intelligence contractor Edward Snowden, who revealed a National Security Agency program to gather data about millions of Americans’ phone calls (though not the content) from phone companies.

Wickr, a San Francisco-based company that provides an encrypted text message service to more than 4 million users, planted a warrant canary in its transparency report in the summer of 2013, becoming the first company, it said, to do so. The report said, “If the canary flies the coop, the tone of this report will change as well because things will have shifted.”

The idea, said Wickr general counsel Jennifer DeTrani in an interview earlier this year, was “to provide more transparency in a way that hadn’t been prohibited.”

The Justice Department’s new guidance in January followed discussions with Facebook, Google, LinkedIn, Microsoft and Yahoo over how to reach a negotiated agreement in exchange for dropping a lawsuit. The guidance stated that the policy on the disclosure of national security requests applied not only to the firms but to all “similarly situated” companies. But that phrase, while presumably referring to online firms that provide communication or storage services, was not spelled out.

Twitter alleged that by holding it to the agreement, the government had violated its constitutional rights.

“The ability to tell people what we’ve done in response to government requests, but importantly, to also tell people what we haven’t done, reflects our ability to be transparent and to express ourselves,” said Colin Crowell, Twitter vice president of global public policy.

“Any situation where the government has the ability to speak and we are severely constrained in our ability to speak on an issue that’s part of the civic debate — not only in the United States but around the world — infringes on our First Amendment rights,” said Crowell, whose job entails dealing with regulatory agencies around the world that are, in the wake of surveillance disclosures, highly skeptical of U.S. companies’ cooperation with the government.

The deal between the tech companies and the Justice Department came together within a few weeks beginning in late December under intense pressure from the White House, which wanted to address companies’ demands that they be able to report more fully on the scope of national security requests.

At the time, the companies were upset that the Snowden disclosures had diminished customer trust and were eager to show their participation with the government was limited. National security officials were adamant they not give away too much information. The FBI, in particular, opposed the idea of allowing firms to indicate they had not received any orders.

A deal was reached in principle on the eve of President Obama’s Jan. 17 speech on surveillance reform. He announced it in his speech.

Eugene Volokh, a UCLA School of Law professor, said the issue of where to draw the line between free speech and national security is a “genuinely difficult” one, especially in the midst of an ongoing national discussion about the proper scope of surveillance.

Volokh earlier this year filed an amicus brief in federal appeals court in support of two unnamed tech firms, represented by the Electronic Frontier Foundation, which have sued the government over their right to disclose receipt of national security letters.

“It’s hard to have a sensible debate about surveillance if you can’t even discuss the magnitude of it,” Volokh said. In the end, he said, “This is one of those important foundational First Amendment questions that really do need to be decided by the Supreme Court.”