Tasmanian police will charge 18 anti-logging activists who stopped work at timber mill in the state's south.

About 40 protesters blocked access to the Ta Ann mill near Judbury in the Huon Valley.

Jenny Weber from the Huon Valley Environment Centre says the protest coincided with a tree sit that has stopped logging in the Esperance forest.

"Ta Ann is still receiving a controversial wood supply and selling that on the international market," she said.

Deputy Premier Bryan Green says Ms Weber's group is wrong.

"They are just wreckers, fringe, and I think in this case liars," he said.

It is the second time in a week Ta Ann has been targeted. The company says it is disappointed.

Ta Ann says the wood currently sourced to its two Tasmanian mills is in full compliance with the forest peace agreement.

Greens leader Nick McKim has called for calm, telling the protesters to consider the "big picture for forest protection".

"Anyone who wants Tasmania's high conservation forests protected from logging needs to consider whether this form of protest is ultimately counterproductive," he said.

Police say the 18 protesters will be charged with trespass by summons.

One of the 40 activists used a bike lock to stop log trucks entering the front gate, while another three who jumped the fence chained themselves to machinery.

Peace deal uncertainty

The most vocal Upper House opponent of Tasmania's forestry peace deal is seriously concerned about the latest protest actions and is weighing up his position on the enacting legislation.

The deal can be killed off if a majority of Upper House MPs do not think the agreement to stabilise the industry is working.

Huon MLC Paul Harriss says recent protests against veneer processor Ta Ann Tasmania are not a good sign.

But the outspoken opponent is not saying how he will react in Parliament.

"I'm seriously concerned whether this whole process will in the end deliver what it set out to deliver," he said.

Mr Green believes the historic agreement will hold.

"I don't think people are going to be sucked in by it."

MLCs have until the end of September to make a move if they want to rip up the peace deal legislation.