Unions ACT secretary Alex White said reports of the rising level of tax breaks delivered to Canberra's property developers illustrated the "excessive greed" of some in the industry.

The tax breaks, or remissions, allow developers to reduce their lease variation charges on blocks of land they apply to change the use of, under criteria for 'economic stimulus' or environmental grounds, or both.

It means the government has effectively foregone $25 million worth of revenue from the property industry since the remissions scheme came into effect in 2014.

Mr White said that what was driving the rising land prices for such blocks was actually public investment in projects like light rail and other infrastructure, but that the industry was still trying to reduce the tax it paid, showing that "no amount of profit is too much".

He said the tax was one of the few ways taxpayers could recoup the increase in the value of land caused by public investments, and the profits should be going back to taxpayers.

"It's very disappointing that at the same time the government says there's no money to support migrant workers getting ripped off, or no money for extra work safety inspectors, all of those causes that we are told there's no money for, that the government is giving the richest industry in town these tax breaks," he said.

"It also shows the political power the industry has, that they don't even have to lobby for laws to change, they get given money for free."

ACT Property Council's Adina Cirson has said the industry backs the lease variation charge (LVC) remissions, but that developers believe it could be better targeted.

"The economic stimulus measures that include remissions on LVC are aimed at increasing building and construction activity. This in turns creates jobs - which is good for all Canberrans and the economy. That's why Unions ACT's position is nonsensical - they should have an interest in having their members employed," Ms Cirson said.

"I would have thought they would be supportive of any measure that encourages growth, prosperity and low unemployment."

The government has also begun an internal review of the entire lease variation charge scheme, but has said it will not look at abolishing the tax.

While the economic stimulus measures are expected to end next year, the environmental criteria are expected to remain, and the Greens are pushing for the regime to help create more affordable housing.

But Mr White said Unions ACT had not been approached to contribute to that review and unions would be "strongly opposed" to any increase to remissions, but it was open to the LVC "being improved".

He also rejected the notion that the tax break was needed to stimulate the economy, arguing if the government wanted to do that, it should instead consider direct support to Canberrans to get more people in work.

Mr White also argued that the environmental criteria under the remissions regime should instead be a mandatory criteria for large new developments, and if it remained, it should instead have to be "proven" after a development is complete, instead of before hand.

A spokesman for the ACT Treasurer said the remissions program was designed to support the ACT economy, particularly the construction industry, "through the years of harsh Abbott government cuts".

"This measure encouraged development in the city and kept thousands of construction workers employed. At the same time the government continued our strong investment in frontline services like schools and hospitals – something we would not have been able to do if the ACT's economy had fallen into recession.

"The remission for sustainability standards is available for projects that deliver environmental outcomes over and above the current industry requirements. All new developments must meet core environmental standards but some projects go further in areas like energy efficiency and water use. This remission rewards those who push the envelope on what's possible for sustainable development and provide a pathway for others to follow."