Mr Coe made the pledge during his opposition budget reply speech in the Legislative Assembly on Thursday, extending the party's existing tax reform plans to abolish territory payroll tax.

But Chief Minister Andrew Barr hit out at the proposal and defended Labor's 20-year reforms to abolish stamp duty, claiming the only way the opposition could stop the reforms would be to raise other taxes and fees.

The debate over the government's reform agenda has continued to rage in the Assembly since it began in 2012, as key planks of a review of the tax system, such as abolishing land tax as well as stamp duty and insurance duty, which has already been abolished, have been largely abandoned.

Mr Barr has suggested rates rises will ease somewhat in the next five years, but has also said that once the government runs out of land to sell - some blocks at prices comparable to Sydney - it will then return to raising rates to raise revenue.

Mr Coe told the Assembly when Mr Barr had started the reforms, he had promised it would cost Canberrans no more than a coffee a week, claiming he lied at the time.

But, after Mr Barr raised the claim with Speaker Joy Burch, as saying someone is a liar is unparliamentary language, Mr Coe was forced to withdraw the comment.

Mr Coe's also said he would not raise rates before a new parliamentary term in 2024 if elected in 2020, to seek voters' permission if the need be in 2024.

Despite the opposition's pledge, it seems the Liberals would maintain stamp duty revenue as per the government's current budget, and the specific detail of the opposition's wider agenda on taxes, fees and charges remains unclear.

Mr Coe told the Assembly that 18 years of Labor governments in the territory had deliberately driven up the cost of land, leaving renters and home owners footing the bill.

He also cited Anglicare and ACT Council of Social Service research claiming the flow on effect of rising rates and land prices had driven thousands of Canberrans into poverty and homelessness.

"Is it right just to govern for those who can afford it?" he said.

"Is it right to ignore the thousands of working poor in this city?

"After 18 years of Labor, you get 8000 kids living below the poverty line ... 8000 kids living in poverty.

"This year, the Smith Family received 2000 requests for help to get kids to school ... but how many were too proud to ask?"

But Mr Barr claimed Mr Coe's plans would mean cutting the equivalent of one third of the government's total health spend every single year.

He said more than 90 per cent of territory businesses already paid no payroll tax, given the ACT's comparably high threshold compared to NSW.

"Mr Coe has also showed yet again that he is willing to blatantly lie when the facts don't fit with his constant negativity about Canberra's economy and tax reform,"

Greens leader Shane Rattenbury also responded to the budget he signed off on as part of cabinet, criticising the government's spending on road infrastructure.

He told the Assembly the minor party had some wins, from more funding for tree planting to a new justice package, but they wanted greater emphasis on climate change.

"Every budget should be a climate change budget," he said.

But Roads Minister Chris Steel later defended spending on roads as vital to the city's future.