The Morrison government’s new encryption bill uses “a sledgehammer to crack a nut” and would capture minor offences dealt with in local courts, as well as potentially allowing law enforcement agencies to target journalists and whistleblowers, experts have warned.

The controversial encryption legislation was passed on the final sitting day of the year last week after Labor gave in to pressure from the government to pass the new laws before Christmas.

It gives law enforcement agencies new powers to intercept encrypted communications on applications such as Signal, Whatsapp and Wickr, which were previously off-limits.

The prime minister, Scott Morrison, and the home affairs minister, Peter Dutton, have repeatedly described the targets of the new law as terrorists, paedophiles and organised criminals.

But the bill also covers any state or commonwealth offences punishable by a term of three years or more in prison, leading experts to warn it will make it possible for police to target people suspected of a wide range of minor offences.

The incoming president of the Law Council of Australia, Arthur Moses SC, told Guardian Australia the legislation was neither “appropriate or proportionate”, pointing out that in some jurisdictions it would cover matters dealt with in a local court.

“Three years is not even a serious indictable offence in New South Wales – a serious indictable offence carries with it five years imprisonment,” he said. “Offences carrying three years maximum penalty are dealt with to finality in the local court.

“So the three-year threshold wouldn’t capture, for example, a common assault, which carries a maximum of two years, but would capture assault occasioning actual bodily harm, which carries with it a maximum of five years.

“Accordingly, it would capture an assault that leaves someone with a bruise.”

The bill has also raised the concerns of the journalists’ union, the Media Entertainment and Arts Alliance.

Earlier in 2018, the government introduced new national security legislation including the Espionage and Foreign Interference Act, which makes it unlawful for a current or former public servant to communicate information that “is likely to cause harm to Australia’s interests” – including its foreign or economic relations.

The offence can be punished by seven years in prison.

“It’s certainly not clear to us that there’s any additional protections for journalists and their sources in this legislation,” the head of the union, Paul Murphy, told Guardian Australia.

“The bar for accessing the information is far too low and the supervision is inadequate. There should be a proper and robust judicial oversight for this and all the national security legislation that we’ve been deluged with in recent years.”

The law could also be applied differently depending on state statues. In NSW, for example, accessing an unlawful abortion is still a criminal offence punishable by up to 10 years jail, and unlawfully supplying a drug or instrument for an abortion is also punishable by up to five years’ imprisonment.

Moses said the Law Council had pushed for a seven-year threshold in order to exclude minor offences from the law’s scope but said it appeared the issue had not been properly considered “in the rush to get this through parliament”.

“The high court has repeatedly observed that there must be proportionality in relation to legislation that impacts on the rights of individuals,” he said.

“You don’t use a sledgehammer to crack a nut. These type of unintended consequences in legislation occur when there is the politicisation of debates concerning national security and people are not focussed on whether legislation is fit for purpose or appropriate.”

He said he hoped “cooler heads will prevail” when the parliament resumes in February, saying the legislation “appears to have gone down a track that was neither necessary nor would it appear intended”.