Spokesman Vica Bayley said yesterday the society would only support a pulp mill if it was subject to a transparent approval process and had community support.

The Wilderness Society, as a signatory to the Tasmanian Forests Statement of Principles, supports "a pulp mill" but Mr Bayley said this was in no way support for the Tamar Valley proposal.

"The Wilderness Society opposes the Tamar Valley pulp mill because of the mill's likely impact on the marine environment, wood supply, location, fresh water use and the discredited fast-track assessment process," he said.

"If the timber industry and the government want a pulp mill to ensure a sustainable timber industry is viable into the future, then they must bring the community along with them."

A decision on the Gunns pulp mill final environmental approvals was expected on Thursday but the company sought tougher environmental controls and Environment Minister Tony Burke extended the deadline until March 10.

The Tasmanian Greens also remain opposed to the proposal, with cabinet minister and Greens MHA Cassy O'Connor calling on Mr Burke to reject the project and Bass Greens MHA Kim Booth threatening to bring down the minority Labor government if it supports the project.

Gunns has refused to detail the stricter controls it has sought but managing director Greg L'Estrange has said the company wanted to build the mill using the best available technology and with the best environmental controls available.

Industry analyst Robert Eastment said it would most likely be tougher emissions measurements and monitoring.

"It's probably reflective of the new management at Gunns," he said.

But Mr Eastment said it would have little impact on the public's opinions of the mill.