Lawyers, unions and civil libertarians yesterday warned that the impact of the tough new penalties, designed to deter anti-forestry protesters, went much further than flagged.

Law Society of Tasmania president Anthony Mihal said people at big rallies where they blocked the road could be charged under the new crime if they blocked any work vehicles such as trucks and taxis from getting through.

Mr Mihal said it was also possible that an employee who had an argument with the boss, refused to leave and then got in the way of a colleague getting to the photocopier could be slapped with a $2000 fine.

Under the legislation, which must still be approved by the Legislative Council, first-time offenders will get a $2000 fine, which could rise to $5000 if challenged in court.

A repeat offender will face a mandatory three-month jail sentence.

Environmental activists, including Ali Alishah, who has spent months in Risdon Prison for his protest action, were in Parliament yesterday to watch the debate over the legislation, which continued late last night.

One was ejected for unfurling a banner in the public gallery.

Greens leader Kim Booth said it was the worst piece of legislation he had seen debated in Parliament since being elected.

Unions Tasmania secretary Kevin Harkins said it was a move to silence criticism.

"This is likely to mean any anti- government protest, including those in relation to the recent federal budget, will now be illegal," Mr Harkins said.

Resources Minister Paul Harriss defended the legislation and said it would not stop peaceful protests.

"It will protect Tasmanian workers from the attacks on their businesses and their livelihoods that they have had to tolerate for too long," Mr Harriss said.