The Enquirer revealed last week that O’Rourke is in advanced talks to sell the plant at Uddingston to FP McCann.
The factory produces precast concrete under the Bison brand.
Chairman and chief executive Ray O’Rourke is a passionate advocate of offsite manufacturing.
The factory is also just 40 miles from Edinburgh where O’Rourke has recently started on a £1bn contract to revamp the St James Centre.
One contractor said: “Ray gave an interview this month going on again about offsite construction being the future of the industry.
“Then just days later they confirm the sale of a precast concrete plant which has left a lot of people scratching their heads.”
Another added: “It’s also a bit baffling when you consider that they have recently picked-up a massive job at at the St James Centre just down the road.
“Why would you sell a plant which is so near and would be so handy to supply precast components for the job?”
Laing O’Rourke declined to comment.