A Dunedin contractor says a video showing one of its workers urging his colleague to run down a cyclist is ''extremely embarrassing'', and it has launched an investigation.

The expletive-laden video showed two employees of Clearwater Civil sitting in the cab of their truck as they travelled behind a cyclist in Portobello Rd on the Otago Peninsula.

It was filmed by the employee sitting on the passenger side of the truck, who urges the driver to run over the cyclist, before unleashing a torrent of abuse at the unwitting rider.

"Run him over Greg mate ... do it.

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"Out of the way you f****** cabbage."

The video was posted on a Dunedin social media page by a Clearwater Civil employee, before it was downloaded by another cyclist and supplied to the Otago Daily Times.

A Clearwater Civil spokesman said the video was ''completely contrary to the culture we try to build in our team,'' and it had launched an investigation.

''The video is extremely embarrassing.

''The allegation is viewed very seriously and there is an employment investigation under way.''

The spokesman said he was pleased it appeared the driver had shown proper consideration, slowing to accommodate the cyclist on the narrow road.

The man who supplied the video said he had spoken to the owner of the excavating contractor and his concerns were taken ''professionally and seriously'' by the company.

A regular rider on the road, the man said recent comments on a Dunedin social media page about cyclists were disturbing, and the video showed the depth of anti-cyclist sentiment among some motorists.

"Most of the comments were along the lines of a lynch mob mentality.

"As a regular road cyclist this makes me even more nervous on the road with these type of drivers out there."