One in four call centre workers has had access to a toilet break restricted, highlighting a "significant risk" to their health and safety, according to a new report.
A study of almost 800 workers by Unison found they often could not take measures to protect their health and wellbeing because of pressurised, target-driven and closely monitored working arrangements.
Almost seven out of 10 of those surveyed said they suffered eye strain and over half had problems with their hearing and voices.
More than 80% said their work caused them to feel stressed, sometimes impacting on their personal lives.
Unison general secretary Dave Prentis said: "The alarming number of health problems highlighted by the survey shows why health and safety matters, and the folly of this Government's constant attacks on health and safety and the cuts in inspections in workplaces such as call centres.
"That this survey has shown more than a quarter have had their basic right to a toilet break restricted or monitored is bad enough, but the physical toll on call workers' eyes, ears and voices - the tools of their trade - is something that managers and organisations cannot ignore.
"Workers rightly expect their employers to have a duty of care not only to their physical health, but also to their mental wellbeing, and the findings of this survey - that eight in 10 are experiencing stress, a quarter of them to a damaging degree - must be addressed urgently.
"The results of this survey should be a wake-up call for call centre employers, and Unison demands that they act now before the situation gets even worse."