Almost half of workplaces have never had a health and safety inspection, a new report shows.
A survey of union reps by the TUC revealed that only one in four said there had been a visit by a health and safety inspector in the past year.
The union organisation said the findings come amid cuts to the Health and Safety Executive (HSE) as well as reductions in workplace inspections by local authorities.
TUC general secretary Frances O'Grady said: "It's deeply worrying that nearly half of health and safety reps say their workplace has never been inspected by the HSE.
"I am appalled that 80% of reps in construction say their workplaces haven't been inspected. Construction workplaces can be some of the most dangerous places to work.
"Huge cuts to the HSE and to local authorities continue to undermine vital safety protections at work. That means more workers at risk of accidents in unsafe workplaces every day. It's time to fund the HSE properly and make sure bosses know that they can't get away with chancing workers' lives in dangerous workplaces."
The TUC has attacked the Government for appointing a former employer to a seat on the board of the HSE reserved for a workers' representative.
A spokesman for the Health and Safety Executive said: "We regulate approximately 900,000 premises fixed worksites and 500,000 transient ones (ie construction sites) which employ over 13 million workers, including offshore installations, manufacturing, construction, agriculture, health services, utilities and many more.
"Through improved targeting we have been able to direct inspectors to the right places, tackling more serious risks. HSE does not measure its impact simply by counting the number of proactive inspections, and never has.
"In addition to planned inspections, HSE directly intervenes with organisations through its response to worker concerns about unsafe activities, it investigates cases of ill health and injury and takes enforcement action where appropriate.
"There is a significant programme of proactive inspections to high-hazard establishments alongside a range of other interventions focused on awareness raising, guidance and joint working."