Hairdressers, cleaners and construction workers are being told they have to become self-employed so their employer could avoid the costs of sick, holiday or maternity pay, it has been revealed.
Callers to the helpline of the conciliation service Acas also disclosed that offers of work dried up if they became pregnant or had a serious illness.
Some workers who fell out with their manager were not sure if they had been sacked or simply left out of a rota temporarily.
There was also uncertainty about being paid while travelling or on call.
Acas said the calls showed there was "confusion and uncertainty" about employment status and rights for those on zero-hours contracts, self-employed or those in the gig economy.
Acas published details of the helpline calls as part of its response to the review into employment currently being undertaken for the government by Matthew Taylor.
Sir Brendan Barber, who chairs Acas, said: "Our helpline analysis revealed that many callers were in a zero-hours, agency or self-employed arrangement out of necessity, rather than by choice, with some people feeling taken advantage of and unfairly excluded from employment rights.
"Many people have also called us for advice on how to challenge their employment status following recent high-profile tribunal decisions that certain individuals should be defined as workers and not as self-employed.
"These types of working arrangements can offer flexibility to individuals and employers, but it is clear that there can be a lot of confusion around employment rights and feelings of insecurity within these non-traditional types of working."