The Scottish Executive has ruled out any immediate change to the boundaries of the Cairngorm National Park.
The bill would extend the national park's boundaries
The SNP's John Swinney has brought forward a bill which would extend the border to take in Blair Atholl and the northern part of Glenshee.
However, Deputy Environment Minister Sarah Boyack told MSPs that the change would disrupt the working of the park.
She said the boundaries would be one of the issues considered next year in the park's five-year review.
Holyrood's environment committee has been taking evidence on the bill brought forward by Mr Swinney, the MSP for North Tayside.
The park currently stretches from Grantown-on-Spey in the north to the Drumochter Hills in the south.
Mr Swinney said that boundary had effectively sliced several important mountains in two.
Calls for the expansion are backed by the Perthshire Alliance for the Real Cairngorms (Parc), which brings together a number of local and national bodies.
However, Scottish Natural Heritage has said it is not convinced of the case for a change at this stage.
Ms Boyack told the committee that she also felt the time was not right for such a move.
She predicted that it would cost up to £150,000 to extend the boundary into Highland Perthshire.
The minister added that the decision to exclude these areas had been taken after lengthy debate.
"The reasons for designation in 2002 weren't taken on a whim and it certainly wasn't a decision taken lightly," Ms Boyack told MSPs.
"I'm very struck by having read the evidence that was given to you last week that many people were not aware in Blair Atholl of those reasons."
She said these included fears over the size of the park and its manageability by a single authority.
Setting out her opposition to a change in boundaries, Ms Boyack said: "Firstly, it would be damaging to the park authority's work.
"Secondly, it would have an impact on the national park plan.
"And thirdly, it would prevent the park's authority completing the local plan for the national park until such time the national park is actually in place and approved."