Many are working when sick, working unpaid overtime and going throughout the year without a paid holiday, the IOSH-commissioned Opinium survey found.
From health advice and counselling to fire safety inductions and the issue of personal protective equipment, non-permanent workers say they come out second best.
With companies such as Uber and Deliveroo in the news for the way they employ gig workers, and the publication in July of the Government-commissioned Taylor Review into modern work practices, the employment or hiring of non-permanent workers is under scrutiny.
With two government select committees set to report back on modern work practices following his review, Matthew Taylor backed IOSH's call for a 'day one agreement' between employer and non-permanent worker that includes a pledge to protect the worker's health and wellbeing.
IOSH director of strategic development Shelley Frost said: "Workplace health risks don't discriminate according to your employment status. When you think of work-related stress, fire risk -- these are all posing the same threat to permanent and non-permanent workers.
"There shouldn't be discrepancies between permanent employees and non-permanent workers in employers' measures to safeguard their safety, health and wellbeing.
"When it responds to the Taylor Review, we want the Government to consider these findings and the very real health risks faced by workers outside of permanent, full-time employment.
"We would welcome up-front agreements between employers and non-permanent workers that set out the same level of care for their health and wellbeing as permanent employees, and linked to their role."
Key findings from the IOSH-Opinium online survey of 500 non-permanent workers:
Two-thirds are working without sick pay (64%), with a half of these working when sick to ensure they are paid -- one respondent reported being sent into work by her employer while suffering with the norovirus
43% are working without holiday pay -- with many relinquishing holiday to ensure they are paid
A quarter of respondents are working unpaid overtime
A third of non-permanent workers have access to occupational health support compared to more than half (54%) of their permanent colleagues
One half (53%) receive a full induction process, including fire exits, compared to two-thirds of their full-time, permanent co-workers
Two-thirds of non-permanent workers and three quarters of business leaders interviewed believe that more needs to be done in the education system to prepare young people for the new world of work
Respondents showed strong support for an up-front agreement between employer and non-permanent worker, with parity on workplace precautions for health and wellbeing being the most important feature (89%)
Mr Taylor, Royal Society of Arts CEO and ex-adviser to former PM Tony Blair, said: "This survey demonstrates that there should not be any barriers to flexible workers enjoying the same standards of safety and health as their permanent colleagues. Often it is as much down to the carelessness or thoughtlessness of the employer.
"Of course, there are cowboys, there's bad practice. What's happening is that people don't think enough or care enough that flexible workers are covered."
The Department for Work and Pensions and Business, Energy and Industrial Strategy select committees are set to report back to Government with recommendations following Good Work: The Taylor Review of Modern Working Practices.
"To incorporate health, safety and wellbeing in the day one agreement is a good idea and I'm sure the select committees will agree with that," said Mr Taylor.
"It must be kept simple, not going into the specifications, but a statement that good health and safety provision applies."
MA student and gig worker Steph Hartland, 21, said: "My current company provides excellent training and really make sure that you are able to do your job well before you start, they encourage you to provide feedback on your clients to make sure it's a positive working experience for everyone involved. They also host Christmas parties, which means you really get to know them well, which creates really positive working relationships.
"By contrast my previous employer really just didn't care, they made me feel like just a piece in a puzzle, they were totally disconnected from their staff, and really made you feel awful. After I was forced to work with the noro-virus, and had to go home, for a long time after they didn't give me anymore work."
Matthew Taylor will lead a discussion on the gig economy today at IOSH 2017, the international conference for safety, health and wellbeing specialists.