The US Department of Justice cannot force Apple to provide the FBI with access to a locked iPhone in a routine Brooklyn drug case, a magistrate judge has ruled.

US Magistrate Judge James Orenstein from the United States District Court Eastern District of New York concluded that Apple is not obligated to assist government investigators against its will, and noted that Congress has not adopted legislation that would achieve the result sought by the government.

Orenstein said the government put forward a reading of theAll Writs Act (AWA) that was so expansive as to render the Act unconstitutional.

“The government’s interpretation of the breadth of authority the AWA confers on courts of limited jurisdiction thus raises serious doubts about how such a statute could withstand constitutional scrutiny under the separation-of-powers doctrine,” Orenstein said.

“It is a reading that thoroughly undermines both the legislature’s own prerogative to reject a legislative proposal effectively and efficiently (without the need to affirmatively ban the proposed authority) and the more general protection against tyranny that the founders believed required the careful separation of governmental powers.”

The magistrate judge wrote that the government had previously invoked the AWA 70 times to compel Apple to assist in the past, with Apple currently facing nine cases in four states whereby the government is attempting to use the AWA to force it to unlock 12 devices.

In October, Orenstein invited Apple to challenge the government’s use of a 227-year-old law to compel Apple to help it recover iPhone data in criminal cases. The Cupertino-based computer maker did challenge it, saying in court papers that extracting information from an iPhone “could threaten the trust between Apple and its customers and substantially tarnish the Apple brand”.

Orenstein said that Apple has changed its attitude to AWA orders recently and is within its rights to do so, but added that the company is merely refusing to help, and not stymieing US authorities.

“The government’s complaint is precisely that Apple is doing nothing at all,” the decision said. “Apple is not ‘thwarting’ anything — it is instead merely declining to offer assistance. There may well be some for whom the distinction between a third party’s active obstruction of law enforcement and its passive refusal to help is meaningless as a matter of policy. But it is hardly meaningless as a matter of legal analysis.”

During the case, Magistrate Judge Orenstein asked the lawyers for the Justice Department whether, if its legal argument were successful, a court could use the AWA to force a drug company to supply lethal injections despite the company’s moral objections. Both at the time and in later submissions, Orenstein deemed the government’s answer as being unsatisfactory.

“If the government cannot explain why the authority it seeks here cannot be used, based on the same arguments before this court, to force private citizens to commit what they believe to be the moral equivalent of murder at the government’s behest, that in itself suggests a reason to conclude that the government cannot establish a lack of unreasonable burden,” he wrote.

The government was not helped in its argument by referring to another case in which the Department of Homeland Security was able to bypass passcode security to get at the data it needed.

“The government, having previously stated both that it cannot bypass an Apple’s passcode security without Apple’s help and that it can do so, now says that it depends — and that what it depends on is not just which device and which operating system is in question, but also on which government expert makes the attempt,” Orenstein said.

“What it does establish is simply that the government has made so many conflicting statements in the two cases as to render any single one of them unreliable.”

In summing up, Orenstein said he offered no opinion on the quandary of the government being able to legally access information for the purposes of law enforcement against “equally legitimate societal interests”.

“How best to balance those interests is a matter of critical importance to our society, and the need for an answer becomes more pressing daily, as the tide of technological advance flows ever farther past the boundaries of what seemed possible even a few decades ago,” Orenstein wrote.

A Justice Department spokesman said it plans to appeal.

Apple and its lawyers said they are reading opinion and will comment later.

“Ultimately, the question to be answered in this matter, and in others like it across the country, is not whether the government should be able to force Apple to help it unlock a specific device; it is instead whether the All Writs Act resolves that issue and many others like it yet to come,” Orenstein wrote.

“For the reasons set forth above, I conclude that it does not.”

Orenstein’s written decision gives support to the company’s position in its fight against a California judge’s order that it create specialised software to help the FBI hack into an iPhone linked to the San Bernardino terrorism investigation.