But business and industry bosses remain unequivocal in their support of the proposed laws.

Justice Slicer appeared at upper house briefings into the legislation this morning. 

He expressed serious concern with imposing mandatory prison terms, allowed for under the laws.

Justice Slicer told MLCs the measure contradicted the separation of powers between Parliament and the judiciary.

''It offends every principle of sentencing,'' he said.

Justice Slicer said existing laws were adequate to police protest action and illegal workplace invasions.

''If you've got a problem, or if industry's got a problem, you can solve it without this,'' Justice Slicer said.

''I don't think you can save (this legislation) ... even with the best will in the world.''

Unions Tasmania boss Steve Walsh told MLCs he supported tough measures for those obstructing the state's key industries.

But Mr Walsh said the scope of the proposed laws were far too broad, by including GBEs such as TT-Line and Metro.

Civil Libertarian Richard Griggs told MLCs if the laws were passed it would have a chilling effect.

But Forest Industry Association of Tasmania head Terry Edwards told MLCs current laws against protests were inadequate.

Mr Edwards argued sentencing existing offences was often too lenient, and the legislation was needed. 

Master Builders Association head Michael Kerschbaum said the title of the legislation, Workplaces (Protection from Protestors) Bill, was misleading.

''This is not about protestors, it's about illegal incursions and illegal blockades on sites,'' he said.

The briefings continue.