The Barnett Government has declared war on radical protesters with new laws criminalising thumb-locks, barrel locks or any other way of physically preventing or threatening lawful activity.

The laws - introduced to the Legislative Council last week without fanfare - reverse the onus of proof, carry maximum penalties of two years jail or a $24,000 fine and ensure cost recovery for any police response.

Stung in recent years by campaigns against shark culling, gas processing at James Price Point and, more recently, logging of Mowen Forest in the South West, the Government says it needs enhanced laws to combat evolving tactics of protesters.

The Opposition has warned the wording of the Bill prohibiting the "physical prevention of a lawful activity" is so broad it could capture a range of activities, including sit-in protests at electorate offices or marches that impede traffic.

The laws make intentionally or physically preventing a lawful activity an offence punishable by 12 months jail or a $12,000 fine. Police suspicion is enough to determine the intention was there, which the accused person must disprove in court.

The penalties double when the conduct risks physical harm to anyone, including the accused. It will also be an offence to manufacture or possess any "thing" suspected to be used for physically preventing lawful action.

In introducing the laws, Attorney-General Michael Mischin said protesters commonly poured freezing water on their thumb to shrink and slide it inside a locking device, making it impossible to remove without tools. Barrel locks involved cutting a hole allowing the protester to hold on to something within the barrel. Both risked injury to protesters.

"Releasing protesters from these devices can take a number of days and often requires the use of specialist equipment and/or expertise," Mr Mischin said.

Shadow attorney-general John Quigley said Labor was yet to adopt a party position but he was concerned at the Bill's onus of proof reversal and ramifications for legitimate protest. Greens MLC Lynn MacLaren said the Bill was "jaw-dropping in its overreach". A spokesman said Nationals MPs had no concerns with the Bill so far.

On Tuesday, Margaret River woman Mira Clohessy allegedly used a thumb lock to attach herself to machinery for seven hours, attracting a nuisance charge.

WA Forest Alliance convenor Jess Beckerling said the laws were excessive but would not stop people from defending the environment.