After a court ordered Apple to help federal investigators get into an encrypted iPhone, the company responded with a court filing Thursday that describes the FBI-requested order as illegal, unconstitutional and dangerous.

"No court has ever authorized what the government now seeks, no law supports such unlimited and sweeping use of the judicial process, and the Constitution forbids it," Apple's lawyers wrote in the company's motion to vacate the order.

"The government's request here creates an unprecedented burden on Apple and violates Apple's First Amendment rights against compelled speech," Apple writes, presenting court decisions that treat computer code as speech protected by the First Amendment.

The court order issued by a federal magistrate in California last week instructs Apple to write special software that would remove some security features that prevent the FBI from guessing the PIN code on an iPhone 5C that was used by one of the San Bernardino shooters. Federal agents have been unable to break the phone's encryption, and attempting to guess the password might result in all the data being deleted. So they've asked Apple to develop software they could load on the phone to let them hook up a computer program that would guess the password without the risk of deletion.

The Justice Department, in its own legal filing last week, argues that Apple's new software "never has to come into the government's custody" or be shared with anyone outside the company — and that Apple is refusing to comply out of business and PR concerns and not technical ones.

The company says that it has already dedicated "substantial resources" to helping the FBI investigate the San Bernardino shootings, but that this request goes too far. In its motion to dismiss the court order, Apple's manager of user privacy describes that hypothetical software as "GovtOS" — a special operating system for the government that Apple would not make under any other circumstances. In fact, CEO Tim Cook has called it the software equivalent of cancer.

Creating such software would require extensive resources, Apple notes, especially if the company has to deploy the software repeatedly — as it expects it would.

"The government says: 'Just this once' and 'Just this phone,' " the motion notes. "But the government knows those statements are not true; indeed the government has filed multiple other applications for similar orders, some of which are pending in other courts. ... If this order is permitted to stand, it will only be a matter of days before some other prosecutor, in some other important case, before some other judge, seeks a similar order using this case as precedent."

That's a dangerous precedent, Apple says, and one that would pose an undue burden on the company. Apple also says that the court order is judicial overreach — requesting a new power that only Congress can mandate — and that it violates the company's First Amendment and Fifth Amendment rights.

The Justice Department responded to Apple's motion by saying that a judge reviewed the FBI request and found it both necessary and reasonable. The court order, which was made under the All Writs Act, is narrowly targeted, the department says.

"The Justice Department's approach to investigating and prosecuting crimes has remained the same; the change has come in Apple's recent decision to reverse its long-standing cooperation in complying with All Writs Act orders," spokeswoman Melanie Newman said in a statement.

Though this court filing is a legal challenge to only one government request for help, Apple has stressed that the precedent could span far wider. In fact, a recently unsealed filing in another case showed that Apple has received similar requests from the government to help access data on a dozen devices, including iPhones and iPad.

U.S. attorneys are now due to respond to Apple's filing by March 10. The hearing in the U.S. District Court for the Central District of California is scheduled for March 22.

FBI Director James Comey and Apple's General Counsel Bruce Sewell are slated to testify at a House Judiciary Committee hearing on encryption on March 1.

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