The Farmers and Graziers Association has told Tasmania's a forest peace deal inquiry the legislation gets worse with every change made.

The Upper House inquiry is taking submissions in Launceston for the first and only time.

The association has already given evidence before the committee, but asked for another hearing to address changes to the legislation made by the State

Government in the lead up to the inquiry.

Chief executive Jan Davis said the bill did not provide any certainty for private forest owners because it keeps changing.

Her colleague Bruce Montgomery said he was shocked by the World Heritage Area announcement last week.

He told the inquiry the extra 170,000 hectares will impact on fire, pest and weed control.

"That has enormous implications for farmers if they suddenly find they're right on a boundary with a World Heritage Area," he said.

An angry Michael Hirst, from the pro-forestry group Give It Back, said the committee needed to tear up the deal.

"It's clear as day to us. We've done our part," he said.

The group has vowed to do whatever it takes to stop the deal.