The latest decision by Environment Minister Peter Garrett gave the mill the thumbs up, he said.

Mr Garrett withheld final approval for the mill until studies are carried out on the effects of effluent from the mill on the marine environment. The studies are expected to take two years.

But Mr Hunt said the decision allowed construction to begin during that time.

"Peter Garrett today did his best to hide the fact that he had given the green light for the construction of the Gunns pulp mill in Tasmania," Mr Hunt said.

"Mr Garrett has tried to give the impression he's had nothing to do with the approval of the construction of the pulp mill. Well, today, he gave that approval."

"He might try to run from his decision but he can't hide from it."

Mr Hunt said construction could take the best part of two years, so the mill would be ready to operate when the environmental studies were finished.

Gunns had welcomed Mr Garrett's approval, Mr Hunt said.

The federal Coalition government approved the construction of the mill when they were in office in 2007. Former environment minister Malcolm Turnbull signed off on the project, subject to some environmental conditions.

Mr Garrett is now in charge of checking all those conditions have been met.