UnionsACT will launch an advertising blitz worth tens of thousands of dollars to stop proposed changes to the ACT's compulsory third party insurance scheme.
The new scheme was designed as part of the ACT's first citizen's jury and will replace the existing at-fault, common law scheme.
But unions have expressed fears the jury process was flawed and the new scheme will give insurers too much power.
UnionsACT secretary Alex White said the changes came after years of intense lobbying behind the scenes and would give insurers the ability to deny medical expenses recommended by a doctor, restrict access to compensation and reduce appeal rights.
"Insurance companies are some of the most powerful, profitable companies in Australia and they're misusing their power to rig the system," Mr White said.
"The royal commission showed what happens when we let insurance companies gain too much power over injured people."
The "Drive By Greed" campaign - which will run on television, radio and online until February - follows a similar campaign from personal injury lawyers last year, and also in 2011 when an earlier reform of the CTP scheme was considered.
The unions would not be pinned down on the cost of the campaign, only saying it was in the tens of thousands of dollars.
The Barr government has previously said there would be strict rules in place covering how insurers dealt with injured motorists, with the creation of a new Motor Accident Injuries Commission.
While insurers are required to provide people with information to help them through the scheme, the government would specify the information and its format, the spokeswoman said.
Separately, other union groups have told a Legislative Assembly inquiry into the CTP bill the changes were unfair and would shift the power away from injured people.
The union also expressed concerns about the citizen's jury process used to shape the scheme.
"In the time available, the jury could not reasonably have been expected develop the expertise necessary to understand or deal with the detail in the scheme," the CFMEU said in its submission.
"For example, the 10 per cent whole person impairment threshold for common law claims is a fundament part of the proposed scheme. Having regard to the specialised medico legal knowledge usually applied to the 10 per cent whole person impairment threshold it is profoundly unlikely that jury understood what degree of injury and permanent incapacity is required to meet the 10 per cent threshold."
The CFMEU said the "arbitrary" nature of thresholds were not raised until very late in the jury process.
"It was not explained to the jury how these thresholds work in practice. Such expert advice as was available to the jury was both narrow and managed by the convenors to achieve what appears to us to be a pre-determined outcome," the union said.
The United Firefighters Union called on the proposed scheme to be abandoned.
"It is the wrong option and the wrong stakeholders namely insurance companies benefit," their submission to the inquiry said.
"Imposition of very high injury thresholds which an injured person must satisfy before being eligible to bring a common law claim is a poor decision for the Canberra community and for our members who are often on the road at all hours of the day and night to serve the Canberra community."
The use of a citizen's jury to reform the CTP was described as a "circuit-breaker" by Chief Minister Andrew Barr, who said he received frequent complaints about the high premiums, delayed payouts and scant coverage associated with the current scheme.
However an Australian National University report found the process had been undermined by the government's public statements on the existing scheme, and the close involvement of expert decision makers in the jury's deliberation stage.
One of the 39 jurors also cast doubt on the process, telling the committee the jury had never been given the chance to consider a model that was high in compensation and with high defined benefits.
However other jurors have said the CTP citizens' jury worked because jurors were asked to make a judgement on human values, not the nuances of each scheme.
The Assembly inquiry will report back on the draft legislation next month, before it is introduced into the parliament early next year.