An inspection of construction sites found 30 per cent in Yorkshire and the Humber failed to protect workers properly.
The month-long inspection found dangerous practices in one third of the 141 sites visited by Health and Safety Executive representatives.
One in seven sites was so poor, formal enforcement action was needed.
The focus of the inspection was on health risks, with 35 per cent of the notices served for the mismanagement of asbestos, failure to control exposure to harmful dusts, noise and vibration, and welfare issues.
But it was failure to provide basic safety measures for people working at height that was the most common issue found by inspectors, accounting for 47 per cent of all enforcement notices served.
Inspectors had to stop work on over 20 sites.