Timber Communities Australia has indicated it will lobby Tasmanian MLCs to amend the forest peace deal legislation, now that it has become a signatory.
TCA is the final negotiating group to sign up to the agreement to reduce the native forestry industry and protect half a million hectares of forest from logging.
The Opposition's forestry spokesman Peter Gutwein says the board has ignored the wishes of its membership.
"[That's] exactly the reasons why the Upper House should reject this legislation," he said.
The group's chief executive Jim Adams says becoming a signatory means the TCA can now lobby MLCs to amend the peace deal legislation.
Mr Adams says the bill does not fully reflect the agreement and there is no guarantee of extra funding.
"We want to see those things included," he said.
The Deputy Premier Bryan Green says the Government is willing to consider sensible amendments.
Mr Green, says fewer than 10 per cent of TCA members turned up to weekend meetings to vote on the deal.
"I believe that what that says is that most people just want us to fix this issue and the process that they've embarked upon, and have played an outstanding role," he said.
"I have to say, in working towards this agreement, provides us with that opportunity."