Government figures show Mr Barr last year approved a whopping $13.5 million worth of "remissions" on the tax developers face when they try to change the use of a block of land in the territory.

That compared to just $10,625 in the second half of 2014 for two applications in the first six months after the remissions scheme began operating.

The massive jump in remissions given out to developers in the past two years comes despite the tax continually failing to achieve the estimated revenue it was meant to in successive ACT budgets.

The remissions scheme allows developers to reduce their lease variation charge burden, if they can show the development could provide "economic stimulus" to the territory, and/or the development is of a high environmental standard.

Government figures show that in 2015, Mr Barr approved $1,656,000 in remissions for nine applications, six of which were approved under the economic criteria and three of which were under both economic and environmental criteria.

In 2016, the $13,532,344 worth of remissions Mr Barr approved were for 19 applications, nine of which were under the economic criteria and 10 under both criteria.

And this year, he approved a further $9,869,750 worth of remissions for 14 applications, four under economic measures and 10 under both criteria.

The government has refused to name the specific developers or developments associated with the tax breaks, under privacy provisions in the territory's tax law.

The remissions have been an effort by government to improve the environmental standards of developments, as well as encourage more development in the territory.

But those measures are understood to now be under the microscope as part of an internal government review of the lease variation charge regime, and while the environmental criteria are likely to continue, the stimulus measures will expire in March next year.

Mr Barr's spokesman said the rising number of remissions handed out was due to developers being required to submit their full development applications to qualify, to help ensure building work would start soon after the charges were decided.

"The need to complete this detailed planning work may have prevented some developers from qualifying for the remission early in the life of the scheme," he said.

He said the stimulus measures were made to counter "the harsh cuts of the Tony Abbott government era" and it had "helped prevent our economy going backwards" in the past few years.

ACT Property Council chief executive Adina Cirson said while the industry was "very supportive" of the remissions, she was worried the increase might indicate "the remissions scheme isn't structured as well as it could be".

"Certainly we have argued over a long period that [the lease variation charge] inhibits development and isn't aligned properly with the policy objectives of government," she said.

"So the remissions are an attempt to minimise that, because it encourages development and better quality development, but there becomes a point when they are so frequent we should be asking, 'Is the scheme operating as efficiently as it could?."

Ms Cirson said the rising number of remissions highlighted the need for a wider review of the tax itself, and she believed it was important to complete that work before the stimulus measures expired next year.

"My worry is that the government wants to see more affordable housing, development along transport corridors and the like, so potentially you could argue for further remissions," she said.

"We also would like to see how the scheme can be designed to encourage more affordable housing, it's something we absolutely need to have a conversation about."

Opposition planning spokeswoman Nicole Lawder said the tax remained a "structurally flawed tax which is stifling investment and redevelopment in Canberra" that added significant costs to projects "before they even get off the ground".