Fewer than half of workplaces have put in place adequate social distancing measures, according to new research.
It casts “huge doubt” over Government claims about the safety of returning to work in England, unions are warning.
The TUC said its research suggested that many firms were not taking adequate measures to protect workers from coronavirus, with those working in low-paid and insecure jobs worse affected.
Just under half of 2,100 workers surveyed for the union organisation said their workplaces have introduced safe social distancing.
Fewer than two in five respondents said their employers have carried out Covid-secure risk assessments, and a similar number reported being given adequate personal protective equipment.
The TUC said its findings cast “huge doubt” on Health Secretary Matt Hancock telling people in England the vast majority of workplaces are Covid-secure.
Most workplaces are thought to have taken some measures to deal with the virus, but the TUC said workers believe their employers are not doing enough to protect them.
A third of those surveyed said they were concerned about not being able to socially distance from colleagues, and a similar number were worried their workplace would not be cleaned properly.
TUC general secretary Frances O’Grady said: “Making sure workplaces are safe is key to preventing the spread of Covid-19 and getting our economy back on its feet.
“Rather than trying to bully people back into offices, ministers should change the law to require all employers to publish their risk assessments, and make sure workplaces are safe.
“They should crack down on bad bosses who risk their workers’ lives.
“Big outsourcing companies have failed the UK on Test and Trace, and now this Government is going to give them more money to fail again, on workplace safety.
“Funding for the Health and Safety Executive has been cut by over a third in the past decade.
“The Government should reverse those cuts and provide HSE with sustained funding so they can recruit and train proper workplace inspectors, inspect more workplaces, and prosecute bad bosses who don’t keep their workers safe.
“That’s how we will increase workers’ confidence that workplaces are safe.”