An Apple iPhone 6S is displayed at an Apple store on Chicago. (Kiichiro Sato/AP)

More than 25 major technology firms, media organizations and civil liberties groups are filing briefs this week in support of Apple’s effort to block the U.S. government from forcing the company to help unlock an iPhone used by one of the San Bernardino terrorists.

Microsoft, Verizon, Facebook, Google, Amazon.com and Yahoo are among the tech and telecom giants preparing to file or join friend-of-the-court briefs, according to industry lawyers.

Those involved say the swell of support is unparalleled, especially for a case at the magistrate judge level — the lowest level of the federal court system. The filings also indicate the level of anxiety among companies about the possibility of a legal precedent greatly expanding the limits of what the government can force a company to do in criminal and national security probes.

Meanwhile, law enforcement groups and families of some of the 14 killed in the Dec. 2 attack in San Bernardino, Calif., are filing briefs in support of the government.

At issue is whether prosecutors and the FBI, citing a law that dates to 1789, can force Apple to write computer code to disable a safety feature on an iPhone recovered after the attack, which killed 14 people. The bureau wants to have a chance to crack the phone’s passcode to get at the encrypted contents on the device.

On Feb. 25, Apple filed a motion opposing a court order to help the FBI unlock the iPhone belonging to a San Bernardino shooter. Here's everything you need to know about Apple vs. the FBI. (Jhaan Elker/The Washington Post)

But the industry is concerned.

“They know that if Apple can be forced to do this, they can be forced to do something similar,” said one industry lawyer, who spoke on the condition of anonymity to discuss internal deliberations. He said he thought Apple’s case was strong.

Today it’s the phone from San Bernardino, he said. Tomorrow it might be a Microsoft operating system on a suspect’s tablet. “It’s ‘Write code, please, that helps us break in more easily,’ ” he said. “That’s the headline.”

But opinions are mixed. Some legal experts said that the government appears to have the stronger case. “In general, I think that the FBI is trying to enforce a lawful order that was obtained following a warrant procedure,” said William Banks, a professor of national security law at Syracuse University.

He was referring to the court order issued less than two weeks ago by a magistrate judge in Riverside, Calif., demanding that Apple write code to dismantle a feature that wipes all data from a phone after repeatedly failed tries to enter a password.

Former Justice Department official Jennifer Daskal said both sides are overstating their arguments. “The government is wrong to say this is just about one case,” said Daskal, a law professor at American University. “On the other hand, it is wrong to say that if Apple loses this case, there’s absolutely no limits to what the government can order a company to do” in cases involving encrypted communications.

Nonetheless, both sides are girding for a protracted court fight, one that could make it to the Supreme Court. Friend-of-the-court briefs are due by Friday, and on Apple’s side, a diverse array of groups will argue that the Justice Department’s order is unconstitutional, has no basis in statute and that the issue is one best settled by Congress.

One argument that companies and civil liberties groups are expected to make is that if the government’s order is upheld, then the FBI might be able to order a technology firm to create, say, malicious software to send to a user’s device in the form of a routine update. “That is the third rail for tech companies — to be forced to deliver a software update that breaks the security of the device,” said Alex Abdo, a staff attorney for the American Civil Liberties Union, which is also filing a brief in support of Apple.

Some of the companies are expected to argue that the Constitution’s due-process clause prohibits the government from “conscripting” them into the service of the government to build products for them.

The Reporters Committee for Freedom of the Press and the Electronic Frontier Foundation, a privacy group, are expected to argue that “code is speech” and that the First Amendment bars the government from forcing Apple to write code that would undo safety features it built into its devices. The media concern, industry lawyers said, is that the government could force a news organization to, say, plant a false story to lure out a suspect.

Former National Security Agency general counsel Stewart Baker said “the government isn’t objecting to the message” of the phone’s password, he said. “It’s objecting to the real-world effect of the code.”

There are human rights concerns as well, lawyers said. If a company is forced to build software for the U.S. government, it would potentially be available to a foreign government such as China, which uses surveillance tools to monitor dissidents. Apple, the argument goes, could not refuse to allow the Chinese government access to such a tool without putting its employees in China at risk of retaliation. And if it acquiesces, dissidents and activists in China would be put at risk.

These issues are so important that they should not be left to judicial interpretation, Apple’s supporters argue. “We need 21st-century laws that address 21st-century technology issues,” Microsoft President Brad Smith told lawmakers Thursday. “And we need these laws to be written by Congress.”

Daskal agreed. “These are really hard issues,” she said, “and this is really about balancing different security interests against one another.”

Amazon founder Jeffrey P. Bezos owns The Washington Post.