Preparatory work has begun south of Pitlochry for the introduction of the controversial measure aimed at reducing accidents on the road which has claimed around 100 lives in the last eight years.
But campaigners claim the start of the work displays "total contempt" for the parliamentary process, as the Holyrood petitions committee is only due to consider 1000 pages of evidence against speed cameras on April 22.
The pressure group "A9 Average Speed Cameras are not the Answer", has submitted a petition which calls for a full investigation of what they call "flawed" evidence that the Scottish Government has accepted in support of the average speed system. A parliamentary debate is also sought.
The group also says that the start of the work comes as new information on A9 driver behaviour "proves beyond doubt" that the current average speed of the A9 was below the current legal limits, being calculated at 58mph.
This, they claim, rendered the argument that average speed on the A9 was too high, redundant.
The current limits are 70mph on dual carriageway and 60mph on single lanes and the average speed system will mean drivers cannot exceed the limit and then slow down when they spot a camera.
The group also claims that far from dealing with A9 safety, the Scottish Government and Transport Scotland were more focused on spending hundreds of thousands of pounds upgrading slip roads on the A9 for this year's Ryder Cup golf competition at Gleneagles, while one of the A9's most deadly junctions at Auchterarder a few miles away has received no attention to upgrade it at all, despite numerous deaths.
Mike Burns, founder of the pressure group, said "We are now in the ludicrous situation of an SNP Government ignoring the evidence, commissioning new reports to suit themselves and ignoring parliamentary process over the A9.
"With more revelations to come over the next few days on the sub standard reports used by Transport Scotland, the SNP must show proper leadership and cancel this flawed project to regain voters' trust in the Highlands as opposed to continuing with south-over-north transport policies."
But a Transport Scotland spokeswoman said the A9 Safety Group, made up of leading businesses using the road, police, local councils, hauliers, and motoring organisations, firmly believed that average speed cameras would save lives on the A9. "We have committed to having the system installed by October and we have to start work now to meet that deadline.
"In the meantime however, our engagement with the public petitions committee will continue, and we will make every effort to explain our compelling evidence base to members.
"We understand that there has been a great deal of discussion about this measure but we have to trust the evidence from across the world which demonstrates the effectiveness of cameras on a variety of road types."
A spokesman for trunk road contractors BEAR Scotland said: "Works on the A9 safety cameras have begun at Pitlochry. Initial work has included the excavation of foundations and trenching for the safety camera infrastructure."
There will be 28 weeks of work. Cameras will be installed at 27 sites along the route between Perth and Inverness within seven distinct average speed camera zones, all of which will be on sections of single carriageway.