The federal government has given timber company Gunns until January next year to complete an environmental impact management plan for its controversial pulp mill in northern Tasmania.

The plan - due to be submitted by October 4 - is only a quarter of the way completed.

The mill was given the go-ahead, subject to 48 approval conditions, last year by the previous Howard government.

Environment Minister Peter Garrett said Gunns had sought an extension to the October 4 deadline. Gunns shares closed 3.2%, or 4.5 cents, higher at $1.445.

After ''careful and thorough consideration'' he had agreed to extend the deadline to January 5, 2009.
 
The plan required a ''thorough and rigorous examination'' of the issues surrounding the proposed mill.

''It is not unusual for major projects to need additional time to ensure that all environmental matters are fully investigated and properly addressed,'' Mr Garrett said in a statement.

The comprehensive assessment of every aspect of the Gunns plan must not be rushed, he said.

The Australian Greens, though, described the extension as ``unjustified'' a decision to allow timber company Gunns more time to prepare an environmental impact management plan for its controversial pulp mill in northern Tasmania.

''Minister Garrett had absolute discretion on this issue,'' Greens senator Christine Milne said in a statement.

''He had no legal obligation to extend the deadline, and no justification for doing so.''

Gunns knew the plan had to be completed within 12 months of the approval, Senator Milne said.

''And they failed to meet that deadline.

''The fact that minister Garrett suggested to Gunns that they might apply for an extension demonstrates that the Rudd government is still captive to Gunns, to the native forest logging industry, and to big business.''

It was impossible to escape the conclusion the government was ``bending over backwards'' to facilitate Gunns, Senator Milne said.

''Gunns has held successive state and federal governments to ransom and made fools of them.

''It is time to end this sorry saga once and for all and let Tasmania move ahead into our clean, green and clever future,'' she said.

AAP