Unions say a plan to enable police to order people in picket lines and blockades to "move on", and arrest those who do not, erodes the right to political protest.

The Coalition introduced reforms on Wednesday extending police powers to issue "move on" orders to people who prevent access to buildings, commit offences in public places, cause others to have a "reasonable fear of violence" or who behave in ways "likely to cause damage to property."

Police would be able to ask such people for their names and addresses, and arrest and fine those who do not comply $720 under the new law. They could also apply to the Magistrates' Court for an exclusion order, banning protesters from entering certain places if they have been given more than one "move on" order in the same place.

ACTU President Ged Kearney said the proposed changes were excessive and unnecessary: "Current legislative provisions governing industrial action are comprehensive and effective for unions and employers."

Employers can apply to the Federal Court to stop unions and individuals from taking unprotected industrial action and personally sue people for pickets which they say harm their businesses.

Ms Kearney called the bill an "ideological attack on unions" which would erode workers' and their supporters' rights: "The right to protest and take a public political or moral stand is an integral part of a decent and just society and something that Melbournians have done in their tens of thousands over the years."

Liberty Victoria president Jane Dixon, SC, similarly opposed the reforms: "The anti-war demonstrations in the City of Melbourne may well have impacted on shops and businesses in the vicinity but Liberty [Victoria] believes that political protests in public places are an important feature of a functioning democracy."

"Move on" orders were introduced under the former Labor government in 2009 but police cannot currently issue them to people picketing in a place of employment or protesting about a particular issue, including those publicising their views with a banner or placard.

Attorney-General Robert Clark's office said that under the new law, "union-friendly restrictions" would not limit police powers.

Mr Clark said that Victorians had the right to protest and express their views: “However, when individuals resort to unlawful tactics that threaten the livelihood of law-abiding businesses, employees and their families, they must be held to account."

The reforms follow long-running protests, including against the east-west link and builder Grocon.

They come a month after the Abbott government announced it would re-introduce the Australian Building and Construction Commission, which could fine people picketing building sites up to $34,000.