Canberra Liberals leader Alistair Coe described the surge in objections as «unprecedented».
«Canberra households and businesses are obviously hurting as a result of this government’s unfair taxes,” Mr Coe said.
The median number of days to process objections has also nearly tripled.
In 2017-18, an unimproved value objection took a median of 54 days to complete, up to a maximum of 330 days.
But so far in 2018-19, objections have taken a median of 148 days to complete, up to a maximum of 274 days.
«All the while [they are] accruing interest on bills that might not have been paid yet because they are being disputed,” Mr Coe said.
On top of this, the vast majority of unimproved value objections are rejected.
Fifty-seven per cent of objections filed in 2017-18 were rejected, while only 35 per cent were allowed or allowed in part.
Of the objections processed so far in 2018-19, 81 per cent have been rejected while only 12 per cent have been allowed or allowed in part.
Only a few cases proceeded to a formal appeal through the ACT Administrative and Civil Tribunal.
Of the 11 appeals settled in 2017-18, four settled, three were dismissed, three were withdrawn and one is outstanding. None were allowed or allowed in part.
The figures come ahead of the release of the findings of an ACT Legislative Assembly inquiry into commercial rates rises this week.
The inquiry heard commercial property owners were not appealing their valuations in ACAT, because the legal bills could be in the realm of $80,000 to $100,000.
However ACT Chief Minister Andrew Barr told the committee land tax was the least-worst» tax a government could collect.
The ACT is seven years into a 20-year program to phase out taxes like stamp duty in favour of land-based taxes like rates.
And while the reform is supposed to be revenue neutral, increasing land values across large parts of the city have contributed to the pinch felt by Canberrans.
Katie Burgess is a reporter for the Canberra Times, covering ACT politics.