Cable firm CityFibre has been fined £35,000 by the Scottish Road Works Commissioner after a worker stood in a manhole in a busy Edinburgh road protected by two traffic cones.
Commissioner Angus Carmichael said the incident in February "could have resulted in a fatality" and demonstrated the company's "lack of compliance with road works legislation".
A video of the incident in Craiglockhart showed a vehicle swerving around the sub-contractor, who is only half visible to drivers.
He imposed the fine for its "serious failures" to comply with laws in a series of incidents, most in Edinburgh.
The incidents included "endangering road workers and the general public, non-compliance with the reinstatement specification, working without valid notification on the Scottish Road Works Register, a lack of qualifications and not cooperating with the City of Edinburgh Council."
Mr Carmichael said he imposed the penalty after the firm's performance failed to significantly improve over the last year.
He said the findings of CityFibre's investigation into the February incident confirmed it had "systematically failed" to co-operate under the relevant law.
He said: "As the failures are of a very serious nature, compromising both safety and quality, I have decided to impose a significant penalty of £35,000 to send a clear message to all organisations undertaking road works that poor performance is unacceptable.
“CityFibre has provided me with an improvement plan and confirmed they are committed to improving their performance and complying with the legislation in future.”
The firm said after the Craiglockhart incident: "The construction worker shown in the video footage was working for KNNS, a CityFibre contractor.
“We have now invoked an immediate stop to all KNNS works conducted on behalf of CityFibre until the incident is fully investigated alongside KNNS management."
The fine comes days after CityFibre was accused of leaving a trail of destruction by botching hundreds of road repairs.
It was branded the worst offender among utility companies, with the number of botched works blamed on the firm soaring by 49 per cent to 286.
Edinburgh City council transport convener Lesley Hinds said: “This should send a strong message to all public utilities companies that they MUST comply with their statutory duties and carry out roadworks responsibly.
"That said, we still believe there is much more that should be done to tackle consistently poor performance by utilities when digging up and reinstating our roads.
“As a council, we have taken every measure we can to encourage the companies to make improvements, including gaining support for a number of organisations for our Edinburgh Road Works Ahead Agreement, but clearly much more needs to be done.
"We welcome the Scottish Government’s focus on this as part of their review of the Office of the Scottish Road Works Commissioner, and we have contributed in terms of our frustration with the situation here in the capital.”
CityFibre chief executive Greg Mesch said: “As a builder of the UK’s next generation of digital infrastructure, we pride ourselves on maintaining one of the lowest failure rates in the industry.
"It is for this reason we were so disappointed in the reinstatement issues resulting from the speed of our full fibre rollout in Edinburgh.
“We have been working closely with the Scottish Road Works Commissioner, City of Edinburgh Council and our contractors to deliver significant improvement while construction progresses on Edinburgh’s world-class Gigabit City network.
"Our plans are already seeing strong results, with a 91 per cent pass rate recorded for Category A inspections in the first quarter of this year.
“In addition to this improvement, we have also committed to investing a further £35,000 in additional health and safety training for all our project staff and contractors across our 40-plus city footprint.
"We aim always to deliver the swift, safe and thorough construction work our customers expect.
"We will learn, we will improve and we will continue to deliver the infrastructure this country so desperately needs”.