More than half (56%) of UK workers believe they are monitored by their boss at work, research from the TUC claims.
The union said this could take a variety of forms, including monitoring internet use, tracking people's locations and timing toilet breaks.
It said workers feared surveillance data was being used to set unfair targets and "take away autonomy".
TUC boss Frances O'Grady said it threatened to undermine morale.
"Monitoring toilet breaks, tracking every movement and snooping on staff outside of working hours creates fear and distrust," she said.
"New technologies should not be used to whittle away our right to privacy, even when we're at work. Employers should discuss and agree workplace monitoring policies with their workforces - not impose them upon them."
According to the research, the forms of surveillance that are least acceptable to workers are:
- Facial recognition software and mood monitoring (76% against)
- Monitoring social media accounts outside work (69% against)
- Recording a worker's location on portable devices (67% against)
- Monitoring of keyboard strokes (57% against)
However, it found 70% of staff think workplace monitoring will become more common, while only 38% said they felt able to challenge forms of surveillance they felt uncomfortable with.
In one case study provided by the TUC, HGV driver Trevor said the use of monitoring technology had become "a major cause of stress".
He said in-cab cameras allowed his employers to "constantly monitor" driver behaviour, including how often they stopped for breaks and the routes they took.
"At first it was just a tracker system to let the employer see the vehicle's location. That wasn't a problem. But the company kept on stepping up the technology," the driver said.
In another example, Kirsty, a security worker from Yorkshire, said she had discovered colleagues were using CCTV to spy on staff at a supermarket .
The 18-year-old said she discovered colleagues had used a security camera to "zoom in" on a woman's backside.
"She spoke to her manager about what had happened," the TUC said. "But her manager wanted to avoid problems ... and persuaded her not to put in a grievance."
BBC Radio 5 Live has been contacted by individuals concerned about surveillance at work.
Mike in Norfolk said he had asked staff to install what he thought was time management software on computers. "[It] turned out it was tracking all browser activity and could even take a photo of them every 10 minutes to check they were still at their desks! I was a bit shocked and uninstalled," he said.
Lorry drivers said the surveillance they were under was less convert.
"A lot of us now have a camera and microphone pointed straight at us in the cab. It's an invasion of privacy and should be banned," said Gus, one lorry driver.
Another driver, Alan, said the monitoring his firm had introduced left him "stressed out". "When I m driving I more worried about what my driving score is than actually concentrating on driving the lorry," Alan said.
Others warn about using work email and phones for anything not related to the job. T
Tom told of a friend working who once worked in four-strong emergency plumbing team. "They were given works mobile smartphones. Three of the four were sacked for viewing sports and adult sites during working hours. The only reason my mate wasn't sacked as well was because he couldn't work out how to access the sites," Tom said.
Sean from Bristol said: "I had a friend who was investigated and then sacked after a company investigated him and then went through [thousands] of his emails. I think once you're under investigation they can look at any of your company emails. Lesson learned: don't use company email for anything extracurricular."