The abolition of a developer exemption when land tax was extended to cover vacant properties last year has led to buyers of off-the-plan homes being stung with bills for hundreds of dollars.

The Barr government vowed to fix the problem, labelling the bills as an "unintended consequence" of the legislation that was intended to stop landlords sitting on vacant homes.

The government has yet to determine how many people could be eligible for a waiver, but those who have been caught up are being urged to contact the Revenue Office to provide the specifics of their case.

Each case will be considered individually, and any charges that have been imposed as a result of "unintended consequences" will be waived, including the full amount of any penalties for failure to pay or interest that may have occurred, a spokesman for Treasurer Andrew Barr said.

"Given the relatively small potential pool of properties that could be affected, we expect both the number and amount of waivers to be quite small," he said.

The ACT Revenue Office will also delay issuing notices to people who may be affected while the issue is resolved as well.

"Notices will continue to be issued to those who are clearly not impacted, for example genuine landlords who let their properties and those whose properties are vacant long term," the spokesman said.

"Any individual who is clearly not impacted by the changes introduced on 1 July 2018 - such as long term landlords - will be expected to meet their land tax obligations. Failure to meet these obligations may result in the application of penalties in these situations."

The government is also working on legislative amendments to fix the problem, likely in the form of an exemption for a set period.

"The Revenue Office has been working with industry stakeholders find a solution to the problem. That solution will then be taken to the government and ultimately to the Legislative Assembly," Mr Barr's spokesman said.

It would not be the first time the government has had to fix an unintended consequence of the legislation.

Earlier this year the government introduced another exemption for land tax for people who are in nursing homes, hospital, or a mental health facility. The exemption expires after two years, or when the property is occupied or sold.

Asked at the time to explain it was necessary, a government spokeswoman said the existing exemption for compassionate grounds did not give people enough time to sell their properties before being charged.

The issue has also opened a can of worms for property owners who've been charged exorbitant land tax bills for properties that were rented or empty for small periods of time at the beginning of a quarter.

Under the legislation, those owners are liable for a full quarter's land tax, even though the property may have only been rented or vacant for one day. One woman who contacted The Canberra Times was charged $1900 for a property where the tenants left on January 2 and she moved in on January 3.

Asked whether the government would consider introducing a system of apportionment so people only paid charges relative to the period when they had tenants or when the property was empty, Mr Barr's spokesman said: "All options will be considered."

"However, we note that apportionment may still impose a land tax bill on the affected group of taxpayers – in this instance they could be charged for several days or weeks of land tax rather than a full quarter," he said.

The government’s intention is that anyone affected by the unintended consequence of the changes should not pay land tax at all, rather than just a smaller amount of land tax.

Any property owner issued with a land tax bill since 1 July 2018 for a property that they have purchased and moved into without first renting it out, should contact the ACT Revenue Office on 6207 0028 or through the ‘Contact us’ page on the Revenue Office website (www.revenue.act.gov.au).