A team of United Nations experts has expressed concern to the Australian government over tough new anti-protest laws in Tasmania that it says would have a “chilling effect” on freedoms.

The Tasmanian legislation, which is being considered by the state’s upper house, would impose mandatory fines and prison terms on protesters who are deemed to interfere with the operations of a business.

Protesters could face a three-month jail term for a second offence.

A group of experts appointed by the UN’s Human Rights Council has told the federal government the laws would probably breach Australia’s international human rights obligations.

David Kaye, the special rapporteur to the UN on freedom of expression and opinion, told Guardian Australia the laws were so broad that protesters would find it hard to know when they were breaking the law.

“There are also very harsh penalties that criminalise expression,” he said. “Ultimately it will chill expression and people speaking out. In a democratic society like Australia you want to encourage expression and peaceful protest.

“On the face of it, the law has problems that really raise concerns over the obligations that Australia has had to uphold for many years. I’m not sure how the government intends to use this power, but even without a crackdown it is likely to chill behaviour.”

Kaye said the Australian government had yet to respond to the concerns raised by the human rights experts.

Last month, a coalition of 13 legal, Indigenous and environmental groups wrote to the UN to express their dismay at the anti-protest laws, which are seen to be largely aimed at anti-logging activists.

The Tasmanian government dismissed the UN experts’ concerns, calling them “incorrect and founded upon false information”.

Tasmania’s minister for resources, Paul Harriss, said the UN had not been given the full story and that the bill sought to protect businesses from harassment, rather than curtail peaceful protest.

“Unfortunately, it appears the critique is based solely upon misinformation being peddled by the Community Legal Centres Tasmania,” he said.

“Its letter to the UNHCR was co-signed by radical protest groups including the Wilderness Society, Markets for Change and the Bob Brown Foundation.

“It would seem that the special rapporteurs have only heard one side of this debate. Ill-informed criticism serves no purpose except to inflame ignorant debate rather than douse it with fact.”

Harriss said the bill would protect the “right to work” enshrined in the UN’s declaration of human rights.

Ben Bartl, policy officer at Community Legal Centres Tasmania, said trespass laws already in place were there to protect businesses.

“These proposed laws are unnecessary and the UN has confirmed that,” he told Guardian Australia. “This is a damning critique by the UN, they definitely haven’t minced their words. This bill is simply a breach of human rights.

“It’s likely the bill will silence protest. It seems to be part of a trend by the states and territories to crack down on protesters and peaceful assembly. The UN has drawn a line in the sand to say this isn’t acceptable and I’d urge the legislative assembly [Tasmania’s upper house] to consider the findings of the UN rapporteurs.”