The Sustainable Forests Timber Amendment (Timber Harvesting Safety Zones) Bill 2022 passed Victoria's upper house on Thursday evening, with the final vote count 30 to five after Labor and the coalition joined forces.

It will now return to the lower house to be rubber-stamped, before going to Victorian Governor Linda Dessau for royal assent and becoming law.

Under the incoming law, the maximum jail sentence and fines for hindering, obstructing or interfering with timber harvesting operations would be upped to 12 months and more than $21,000.

Other existing rules will be strengthened inside timber harvesting safety zones, small and restricted areas where trees are logged.

Often used in protest activities, PVC and metal pipes will be added to the prohibited items list, with authorised officers given additional powers to search containers, bags and vehicles as well as issue banning notices to repeat offenders.

The Victorian branches of the Maritime Union of Australia, the United Workers Union and Australian Services Union wrote to the state government on Tuesday in a late bid to withdraw the "undemocratic" bill.

"The bill wrongly locates workplace risk in the democratic right to protest," reads the letter to Premier Daniel Andrews, Agriculture Minister Gayle Tierney and Workplace Safety Minister Ingrid Stitt.

"Any stripping away of the right to protest eventually finds its way to further limiting workplace action. Already Australia has some of the most restrictive laws around industrial action in the world.

"In the context of a climate crisis, the right to protest must be advanced not diminished."

Mr Andrews was aware of the letter but insisted the new laws strike the "right balance" between the right to protest and worker safety.

"Some of these work sites ... are potentially very, very dangerous places. They need to be regulated, they need to be safe," he told reporters before the upper house vote.

The changes are based on feedback from workers, many of whom are union members, Mr Andrews said.

Victorian Greens Leader Samantha Ratnam said it was a grim day for Victoria's native forests and democracy.

"This sets a worrying precedent for the right to protest in Victoria," she said.

Despite repeated requests, Ms Ratman said Labor failed to provide any evidence of logging protesters threatening the safety of workers.

The fact a tragedy was yet to occur does not mean the state government should not act to lessen its likelihood, Mr Andrews argued.

"I'm sure there's been near misses ... often these things can be very, very much on the edge," he said.

Australian Associated Press