The vow comes as the fate of the open spaces on Melbourne's urban fringe - predominantly protected for agriculture and conservation - has been contested for at least a decade, with governments from both major parties pushing changes to urban development boundaries.

Opposition planning spokesman Brian Tee will on Tuesday tell the Green Wedges Coalition's annual general meeting the boundaries would not be changed while Labor was in government.

He also said Labor wanted to stop the building of airfields, treatment plants and puppy farms in the wedges. Controls around subdivisions would also be hardened.

"The Liberals have been slowly eating away at our landscapes and soon there'll be nothing left," he said.

But Planning Minister Matthew Guy hit back, telling Fairfax Media the Coalition had done more to protect the green wedges in one term than Labor had in 10 years under the Bracks and Brumby governments.

When asked whether the boundaries would change if the Coalition retained power, Mr Guy said: "No, because the Coalition has put in a permanent boundary."

Early in its term in power, the Coalition considered relaxing limits on development that could occur in green wedges, particularly for tourism and sellers of farming produce.

It sparked criticism from some activists and prominent Victorians, including Lady Hamer, wife of former Victorian Liberal premier Sir Rupert Hamer, who led the establishment of the wedges more than 40 years ago.

Last year, the Napthine government largely stepped backed from the proposed changes to green wedges development rules. But it pushed through more relaxed conditions for other areas known as the rural conservation zone.

RMIT planning professor Michael Buxton said the Napthine government's planning strategy for urban growth was not an enforceable position from which to limit development sprawl.

"Plan Melbourne states the government will introduce a permanent growth boundary, but that has absolutely no force or effect in its current form. It's just a statement or intention from the government," he said.

He accused Mr Guy of not doing enough to boost protection for the wedges. "He [Mr Guy] weakened the green wedge zone protections, not in a major way, but he certainly did not strengthen them," he said.

Professor Buxton said a strict legislative regime had been in place since the Bracks government, requiring both houses of Parliament to vote on changes to the urban boundary. But consecutive governments had continued to chip away at the green wedges, he said.