Ucatt, which represents 125,000 workers, said there had been 51 deaths since April, including a four-week period from late November in which there were eight fatalities.
The union said it had been hoping for a big reduction in deaths and injuries this year, especially after Work and Pensions Secretary Peter Hain launched a safety forum for the industry.
But officials said they feared this year will end with a similar toll to 2006/07 when 77 construction workers died, a 30 per cent increase on the previous 12 months.
Ucatt said a recent trend had seen more workers killed in the second half of the year, suggesting greater demands on workers to carry out exposed work at heights during the winter months.
Traditionally construction companies have attempted to limit this work during the colder months when such work is inevitably riskier, said the union.
General secretary Alan Ritchie said: "Once again far too many construction workers are dying. The vast majority of these deaths are preventable and are caused by lax safety and careless bosses."